--- loncom/interface/statistics/lonproblemstatistics.pm	2004/01/28 14:38:40	1.64
+++ loncom/interface/statistics/lonproblemstatistics.pm	2013/12/30 14:05:21	1.122.2.2
@@ -1,6 +1,6 @@
 # The LearningOnline Network with CAPA
 #
-# $Id: lonproblemstatistics.pm,v 1.64 2004/01/28 14:38:40 matthew Exp $
+# $Id: lonproblemstatistics.pm,v 1.122.2.2 2013/12/30 14:05:21 raeburn Exp $
 #
 # Copyright Michigan State University Board of Trustees
 #
@@ -50,13 +50,21 @@ Excel files, and plots.
 package Apache::lonproblemstatistics;
 
 use strict;
-use Apache::lonnet();
+use Apache::lonnet;
 use Apache::loncommon();
 use Apache::lonhtmlcommon;
 use Apache::loncoursedata;
 use Apache::lonstatistics;
+use LONCAPA::lonmetadata();
 use Apache::lonlocal;
 use Spreadsheet::WriteExcel;
+use Apache::lonstathelpers();
+use Time::HiRes;
+use LONCAPA;
+ 
+
+my @StatsArray;
+my %SeqStat;    # keys are symbs, values are hash refs
 
 ##
 ## Localization notes:
@@ -65,27 +73,75 @@ use Spreadsheet::WriteExcel;
 ## header for plots created with Graph.pm, both of which more than likely do
 ## not support localization.
 ##
+## Additional Notes:
+## Localization can be done and is done before passing the phrases
+## to the output.
+## This might conflict with special characters, e.g. German Umlaute or
+## chinese characters. Do not use such characters in this case.
+## If this failed, consider that the sequence and folder names
+## are also passed to the output and would fail the same way.
+##
+#
+#
+##
+## Description of Field attributes
+##
+## Attribute     Required   Value       Meaning or Use
+##
+## name            yes      any scalar  Used to uniquely identify field
+## title           yes      any scalar  This is what the user sees to identify
+##                                      the field.  Passed through &mt().
+## long_title      yes      any scalar  Used as graph heading and in excel
+##                                      output.  Passed through &mt().
+## align           no    (left|right|center)  HTML cell contents alignment
+## color           yes      html color  HTML cell background color
+##                                      used to visually group statistics
+## special         no          (link)   Indicates a link, target is name.link
+##                                      Currently set in &get_statistics()
+## graphable       no      (yes|no)     Can a bar graph of the field be 
+##                                      produced?
+## sortable        no      (yes|no)     Should a sort link be put in the
+##                                      column header?
+## selectable      yes     (yes|no)     Can the column be removed from the
+##                                      statistics display?
+## selected        yes     (yes|no)     Is the column selected by default?
+##
+## format          no      sprintf format string
+##
+## excel_format    no      excel format type 
+##                               (see &Apache::loncommon::define_excel_formats
 my @Fields = (
            { name => 'problem_num',
              title => 'P#',
              align => 'right',
-             color => '#FFFFE6' },
+             color => '#FFFFE6',
+             selectable => 'no',
+             defaultselected => 'yes',
+           },
            { name   => 'container',
              title  => 'Sequence or Folder',
              align  => 'left',
              color  => '#FFFFE6',
-             sortable => 'yes' },
+             sortable => 'yes',
+             selectable => 'no',
+             defaultselected => 'yes',
+           },
            { name   => 'title',
              title  => 'Title',
              align  => 'left',
              color  => '#FFFFE6',
              special  => 'link',
-             sortable => 'yes', },
-           { name   => 'part', 
+             sortable => 'yes',
+             selectable => 'no',
+             defaultselected => 'yes',
+           },
+           { name   => 'part',
              title  => 'Part',
              align  => 'left',
              color  => '#FFFFE6',
-             },
+             selectable => 'no',
+             defaultselected => 'yes',
+           },
            { name   => 'num_students',
              title  => '#Stdnts',
              align  => 'right',
@@ -93,7 +149,10 @@ my @Fields = (
              format => '%d',
              sortable  => 'yes',
              graphable => 'yes',
-             long_title => 'Number of Students Attempting Problem' },
+             long_title => 'Number of Students Attempting Problem',
+             selectable => 'yes',
+             defaultselected => 'yes',
+           },
            { name   => 'tries',
              title  => 'Tries',
              align  => 'right',
@@ -101,7 +160,10 @@ my @Fields = (
              format => '%d',
              sortable  => 'yes',
              graphable => 'yes',
-             long_title => 'Total Number of Tries' },
+             long_title => 'Total Number of Tries',
+             selectable => 'yes',
+             defaultselected => 'yes',
+           },
            { name   => 'max_tries',
              title  => 'Max Tries',
              align  => 'right',
@@ -109,7 +171,21 @@ my @Fields = (
              format => '%d',
              sortable  => 'yes',
              graphable => 'yes',
-             long_title => 'Maximum Number of Tries' },
+             long_title => 'Maximum Number of Tries',
+             selectable => 'yes',
+             defaultselected => 'yes',
+           },
+           { name   => 'min_tries',
+             title  => 'Min Tries',
+             align  => 'right',
+             color  => '#DDFFFF',
+             format => '%d',
+             sortable  => 'yes',
+             graphable => 'yes',
+             long_title => 'Minumum Number of Tries',
+             selectable => 'yes',
+             defaultselected => 'yes',
+           },
            { name   => 'mean_tries',
              title  => 'Mean Tries',
              align  => 'right',
@@ -117,7 +193,10 @@ my @Fields = (
              format => '%5.2f',
              sortable  => 'yes',
              graphable => 'yes',
-             long_title => 'Average Number of Tries' },
+             long_title => 'Average Number of Tries',
+             selectable => 'yes',
+             defaultselected => 'yes',
+           },
            { name   => 'std_tries',
              title  => 'S.D. tries',
              align  => 'right',
@@ -125,7 +204,10 @@ my @Fields = (
              format => '%5.2f',
              sortable  => 'yes',
              graphable => 'yes',
-             long_title => 'Standard Deviation of Number of Tries' },
+             long_title => 'Standard Deviation of Number of Tries',
+             selectable => 'yes',
+             defaultselected => 'yes',
+           },
            { name   => 'skew_tries',
              title  => 'Skew Tries',
              align  => 'right',
@@ -133,16 +215,10 @@ my @Fields = (
              format => '%5.2f',
              sortable  => 'yes',
              graphable => 'yes',
-             long_title => 'Skew of Number of Tries' },
-           { name   => 'deg_of_diff',
-             title  => 'DoDiff',
-             align  => 'right',
-             color  => '#DDFFFF',
-             format => '%5.2f',
-             sortable  => 'yes',
-             graphable => 'yes',
-             long_title => 'Degree of Difficulty'.
-                           '[ 1 - ((#YES+#yes) / Tries) ]'},
+             long_title => 'Skew of Number of Tries',
+             selectable => 'yes',
+             defaultselected => 'no',
+           },
            { name   => 'num_solved',
              title  => '#YES',
              align  => 'right',
@@ -150,7 +226,10 @@ my @Fields = (
              format => '%4.1f',#             format => '%d',
              sortable  => 'yes',
              graphable => 'yes',
-             long_title => 'Number of Students able to Solve' },
+             long_title => 'Number of Students able to Solve',
+             selectable => 'yes',
+             defaultselected => 'yes',
+           },
            { name   => 'num_override',
              title  => '#yes',
              align  => 'right',
@@ -158,17 +237,367 @@ my @Fields = (
              format => '%4.1f',#             format => '%d',
              sortable  => 'yes',
              graphable => 'yes',
-             long_title => 'Number of Students given Override' },
+             long_title => 'Number of Students given Override',
+             selectable => 'yes',
+             defaultselected => 'yes',
+           },
+           { name   => 'tries_per_correct',
+             title  => 'tries/correct',
+             align  => 'right',
+             color  => '#FFDDDD',
+             format => '%4.1f',
+             sortable  => 'yes',
+             graphable => 'yes',
+             long_title => 'Tries per Correct Answer',
+             selectable => 'yes',
+             defaultselected => 'yes',
+           },
+           { name   => 'num_wrong',
+             title  => '#Wrng',
+             align  => 'right',
+             color  => '#FFDDDD',
+             format => '%4.1f',
+             sortable  => 'yes',
+             graphable => 'yes',
+             long_title => 'Number of students whose final answer is wrong',
+             selectable => 'yes',
+             defaultselected => 'yes',
+           },
            { name   => 'per_wrong',
              title  => '%Wrng',
              align  => 'right',
-             color  => '#FFFFE6',
+             color  => '#FFDDDD',
              format => '%4.1f',
              sortable  => 'yes',
              graphable => 'yes',
-             long_title => 'Percent of students whose final answer is wrong' },
+             long_title => 'Percent of students whose final answer is wrong',
+             selectable => 'yes',
+             defaultselected => 'yes',
+           },
+           { name   => 'deg_of_diff',
+             title  => 'DoDiff',
+             align  => 'right',
+             color  => '#FFFFE6',
+             format => '%5.2f',
+             sortable  => 'yes',
+             graphable => 'yes',
+             long_title => 'Degree of Difficulty'.
+                           ' ~[ 1 - ((#YES+#yes) / Tries) ~]',
+             selectable => 'yes',
+             defaultselected => 'yes',
+           },
+           { name   => 'deg_of_disc',
+             title  => 'DoDisc',
+             align  => 'right',
+             color  => '#FFFFE6',
+             format => '%4.2f',
+             sortable  => 'yes',
+             graphable => 'yes',
+             long_title => 'Degree of Discrimination',
+             selectable => 'yes',
+             defaultselected => 'yes',
+           },
+##   duedate included for research purposes.  Commented out most of the time.
+#           { name => 'duedate',
+#             title => 'Due Date',
+#             align => 'left',
+#             color => '#FFFFFF',
+#             sortable => 'yes',
+#             graphable => 'no',
+#             long_title => 'Due date of resource for instructor',
+#             selectable => 'no',
+#             defaultselected => 'yes',
+#            },
+##   opendate included for research purposes.  Commented out most of the time.
+#           { name => 'opendate',
+#             title => 'Open Date',
+#             align => 'left',
+#             color => '#FFFFFF',
+#             sortable => 'yes',
+#             graphable => 'no',
+#             long_title => 'date resource became answerable',
+#             selectable => 'no',
+#             defaultselected => 'yes',
+#            },
+##   symb included for research purposes.  Commented out most of the time.
+#           { name => 'symb',
+#             title => 'Symb',
+#             align => 'left',
+#             color => '#FFFFFF',
+#             sortable => 'yes',
+#             graphable => 'no',
+#             long_title => 'Unique LON-CAPA identifier for problem',
+#             selectable => 'no',
+#             defaultselected => 'yes',
+#            },
+##   resptypes included for research purposes.  Commented out most of the time.
+#           { name => 'resptypes',
+#             title => 'Response Types',
+#             align => 'left',
+#             color => '#FFFFFF',
+#             sortable => 'no',
+#             graphable => 'no',
+#             long_title => 'Response Types used in this problem',
+#             selectable => 'no',
+#             defaultselected => 'yes',
+#            },
+##   maxtries included for research purposes.  Commented out most of the time.
+#           { name => 'maxtries',
+#             title => 'Maxtries',
+#             align => 'left',
+#             color => '#FFFFFF',
+#             sortable => 'no',
+#             graphable => 'no',
+#             long_title => 'Maximum number of tries',
+#             selectable => 'no',
+#             defaultselected => 'yes',
+#            },
+##   hinttries included for research purposes.  Commented out most of the time.
+#           { name => 'hinttries',
+#             title => 'hinttries',
+#             align => 'left',
+#             color => '#FFFFFF',
+#             sortable => 'no',
+#             graphable => 'no',
+#             long_title => 'Number of tries before a hint appears',
+#             selectable => 'no',
+#             defaultselected => 'yes',
+#            },
+#
+##   problem weight for instructor
+           { name => 'weight',
+             title => 'weight',
+             align => 'right',
+             color => '#FFFFFF',
+             sortable => 'no',
+             graphable => 'no',
+             long_title => 'Problem weight (for instructor)',
+             selectable => 'yes',
+             defaultselected => 'yes',
+            },
 );
 
+my @SeqFields = (
+           { name   => 'title',
+             title  => 'Sequence',
+             align  => 'left',
+             color  => '#FFFFE6',
+             special  => 'no',
+             sortable => 'no',
+             selectable => 'yes',
+             defaultselected => 'no',
+           },
+           { name   => 'items',
+             title  => '#Items',
+             align  => 'right',
+             color  => '#FFFFE6',
+             format => '%4d',
+             sortable  => 'no',
+             graphable => 'no',
+             long_title => 'Number of Items in Sequence',
+             selectable => 'yes',
+             defaultselected => 'no',
+           },
+           { name   => 'scoremean',
+             title  => 'Score Mean',
+             align  => 'right',
+             color  => '#FFFFE6',
+             format => '%4.2f',
+             sortable  => 'no',
+             graphable => 'no',
+             long_title => 'Mean Sequence Score',
+             selectable => 'yes',
+             defaultselected => 'no',
+           },
+           { name   => 'scorestd',
+             title  => 'Score STD',
+             align  => 'right',
+             color  => '#FFFFE6',
+             format => '%4.2f',
+             sortable  => 'no',
+             graphable => 'no',
+             long_title => 'Standard Deviation of Sequence Scores',
+             selectable => 'yes',
+             defaultselected => 'no',
+           },
+           { name   => 'scoremax',
+             title  => 'Score Max',
+             align  => 'right',
+             color  => '#FFFFE6',
+             format => '%4.2f',
+             sortable  => 'no',
+             graphable => 'no',
+             long_title => 'Maximum Sequence Score',
+             selectable => 'yes',
+             defaultselected => 'no',
+           },
+           { name   => 'scoremin',
+             title  => 'Score Min',
+             align  => 'right',
+             color  => '#FFFFE6',
+             format => '%4.2f',
+             sortable  => 'no',
+             graphable => 'no',
+             long_title => 'Minumum Sequence Score',
+             selectable => 'yes',
+             defaultselected => 'no',
+           },
+           { name   => 'scorecount',
+             title  => 'Score N',
+             align  => 'right',
+             color  => '#FFFFE6',
+             format => '%4d',
+             sortable  => 'no',
+             graphable => 'no',
+             long_title => 'Number of Students in score computations',
+             selectable => 'yes',
+             defaultselected => 'no',
+           },
+           { name   => 'countmean',
+             title  => 'Count Mean',
+             align  => 'right',
+             color  => '#FFFFFF',
+             format => '%4.2f',
+             sortable  => 'no',
+             graphable => 'no',
+             long_title => 'Mean Sequence Score',
+             selectable => 'yes',
+             defaultselected => 'no',
+           },
+           { name   => 'countstd',
+             title  => 'Count STD',
+             align  => 'right',
+             color  => '#FFFFFF',
+             format => '%4.2f',
+             sortable  => 'no',
+             graphable => 'no',
+             long_title => 'Standard Deviation of Sequence Scores',
+             selectable => 'yes',
+             defaultselected => 'no',
+           },
+           { name   => 'countmax',
+             title  => 'Count Max',
+             align  => 'right',
+             color  => '#FFFFFF',
+             format => '%4.2f',
+             sortable  => 'no',
+             graphable => 'no',
+             long_title => 'Maximum Number of Correct Problems',
+             selectable => 'yes',
+             defaultselected => 'no',
+           },
+           { name   => 'countmin',
+             title  => 'Count Min',
+             align  => 'right',
+             color  => '#FFFFFF',
+             format => '%4.2f',
+             sortable  => 'no',
+             graphable => 'no',
+             long_title => 'Minumum Number of Correct Problems',
+             selectable => 'yes',
+             defaultselected => 'no',
+           },
+           { name   => 'count',
+             title  => 'Count N',
+             align  => 'right',
+             color  => '#FFFFFF',
+             format => '%4d',
+             sortable  => 'no',
+             graphable => 'no',
+             long_title => 'Number of Students in score computations',
+             selectable => 'yes',
+             defaultselected => 'no',
+           },
+           { name   => 'KR-21',
+             title  => 'KR-21',
+             align  => 'right',
+             color  => '#FFAAAA',
+             format => '%4.2f',
+             sortable  => 'no',
+             graphable => 'no',
+             long_title => 'KR-21 reliability statistic',
+             selectable => 'yes',
+             defaultselected => 'no',
+           },
+);
+
+my %SelectedFields;
+
+sub parse_field_selection {
+    #
+    # Pull out the defaults
+    if (! defined($env{'form.fieldselections'})) {
+        $env{'form.fieldselections'} = [];
+        foreach my $field (@Fields) {
+            next if ($field->{'selectable'} ne 'yes');
+            if ($field->{'defaultselected'} eq 'yes') {
+                push(@{$env{'form.fieldselections'}},$field->{'name'});
+            }
+        }
+    }
+    #
+    # Make sure the data we are plotting is there
+    my %NeededFields;
+    if (exists($env{'form.plot'}) && $env{'form.plot'} ne '' &&
+        $env{'form.plot'} ne 'none') {
+        if ($env{'form.plot'} eq 'degrees') {
+            $NeededFields{'deg_of_diff'}++;
+            $NeededFields{'deg_of_disc'}++;
+        } elsif ($env{'form.plot'} eq 'tries statistics') {
+            $NeededFields{'mean_tries'}++;
+            $NeededFields{'std_tries'}++;
+            $NeededFields{'problem_num'}++;
+        } else {
+            $NeededFields{$env{'form.plot'}}++;
+        }
+    }
+    #
+    # This should not happen, but in case it does...
+    if (ref($env{'form.fieldselections'}) ne 'ARRAY') {
+        $env{'form.fieldselections'} = [$env{'form.fieldselections'}];
+    }
+    #
+    # Set the field data and the selected fields (for easier checking)
+    undef(%SelectedFields);
+    foreach my $field (@Fields) {
+        if ($field->{'selectable'} ne 'yes') {
+            $field->{'selected'} = 'yes';
+        } else {
+            $field->{'selected'} = 'no';
+        }
+        if (exists($NeededFields{$field->{'name'}})) {
+            $field->{'selected'} = 'yes';
+            $SelectedFields{$field->{'name'}}++;
+        }
+        foreach my $selection (@{$env{'form.fieldselections'}}) {
+            if ($selection eq $field->{'name'} || $selection eq 'all') {
+                $field->{'selected'} = 'yes';
+                $SelectedFields{$field->{'name'}}++;
+            }
+        }
+    }
+    #
+    # Always show all the sequence statistics (for now)
+    foreach my $field (@SeqFields) {
+        $field->{'selected'} = 'yes';
+    }
+    return;
+}
+
+sub field_selection_input {
+    my $Str = '<select name="fieldselections" multiple="multiple" size="5">'."\n";
+    $Str .= '<option value="all">all</option>'."\n";
+    foreach my $field (@Fields) {
+        next if ($field->{'selectable'} ne 'yes');
+        $Str .= '    <option value="'.$field->{'name'}.'" ';
+        if ($field->{'selected'} eq 'yes') {
+            $Str .= 'selected ';
+        }
+        $Str .= '>'.$field->{'title'}.'</option>'."\n";
+    }
+    $Str .= "</select>\n";
+}
+
 ###############################################
 ###############################################
 
@@ -183,74 +612,51 @@ select sections, maps, and output.
 
 ###############################################
 ###############################################
-my @OutputOptions = 
-    (
-     { name  => 'problem statistics grouped by sequence',
-       value => 'HTML problem statistics grouped',
-       description => 'Output statistics for the problem parts.',
-       mode => 'html',
-       show => 'grouped',
-     },
-     { name  => 'problem statistics ungrouped',
-       value => 'HTML problem statistics ungrouped',
-       description => 'Output statistics for the problem parts.',
-       mode => 'html',
-       show => 'ungrouped',
-     },
-     { name  => 'problem statistics, Excel',
-       value => 'Excel problem statistics',
-       description => 'Output statistics for the problem parts '.
-           'in an Excel workbook',
-       mode => 'excel',
-       show => 'all',
-     },
-     );
-
 sub CreateInterface {
+    my ($r) = @_;
+    #
+    &parse_field_selection();
+    #
     my $Str = '';
-    $Str .= '<h2>Overall Problem Statistics'.
-        &Apache::loncommon::help_open_topic('Statistics_Overall_Key').
-        '</h2>'."\n";
-    $Str .= '<table cellspacing="5">'."\n";
-    $Str .= '<tr>';
-    $Str .= '<td align="center"><b>'.&mt('Sections').'</b></td>';
-    $Str .= '<td align="center"><b>'.&mt('Enrollment Status').'</b></td>';
-    $Str .= '<td align="center"><b>'.&mt('Sequences and Folders').'</b></td>';
-    $Str .= '<td align="center"><b>'.&mt('Output').'</b></td>';
-    $Str .= '</tr>'."\n";
+    $Str .= '<p>';
+    $Str .= &Apache::loncommon::start_data_table();
+    $Str .= &Apache::loncommon::start_data_table_header_row();
+    $Str .= '<th>'.&mt('Sections').'</th>';
+    $Str .= '<th>'.&mt('Groups').'</th>';
+    $Str .= '<th>'.&mt('Access Status').'</th>';
+    $Str .= '<th>'.&mt('Sequences and Folders').'</th>';
+    $Str .= '<th>'.&mt('Statistics').'</th>';
+    $Str .= '<th>'.&mt('Plot Graph').'</th>';
+    $Str .= '<th>'.&mt('Time Period').'</th>';
+    $Str .= &Apache::loncommon::end_data_table_header_row();
     #
-    $Str .= '<tr><td align="center">'."\n";
+    $Str .= &Apache::loncommon::start_data_table_row();
+    $Str .= '<td align="center" valign="top">'."\n";
     $Str .= &Apache::lonstatistics::SectionSelect('Section','multiple',5);
-    $Str .= '</td><td align="center">';
+    $Str .= '</td><td align="center" valign="top">';
+    $Str .= &Apache::lonstatistics::GroupSelect('Group','multiple',5);
+    $Str .= '</td><td align="center" valign="top">';
     $Str .= &Apache::lonhtmlcommon::StatusOptions(undef,undef,5);
-    $Str .= '</td><td align="center">';
+    $Str .= '</td><td align="center" valign="top">';
     #
-    my $only_seq_with_assessments = sub { 
-        my $s=shift;
-        if ($s->{'num_assess'} < 1) { 
-            return 0;
-        } else { 
-            return 1;
-        }
-    };
-    $Str .= &Apache::lonstatistics::MapSelect('Maps','multiple,all',5,
-                                              $only_seq_with_assessments);
-    $Str .= '</td><td>'."\n";
-    my ($html,$outputmode,$show) = 
-        &Apache::lonstatistics::CreateAndParseOutputSelector(
-                                            'statsoutputmode',
-                                            'HTML problem statistics grouped',
-                                            @OutputOptions);
-    $Str .= $html;
-    $Str .= '</td></tr>'."\n";
-    $Str .= '</table>'."\n";
+    $Str .= &Apache::lonstatistics::map_select('Maps','multiple,all',5);
+    $Str .= '</td><td align="center" valign="top">';
+    $Str .= &field_selection_input();
+    $Str .= '</td><td align="center" valign="top">';
+    $Str .= &plot_dropdown();
+    $Str .= '</td>'."\n";
+    $Str .= '</td><td align="center" valign="top">';
+    $Str .= &Apache::lonstathelpers::limit_by_time_form();
+    $Str .= '</td>'."\n";
+    $Str .=  &Apache::loncommon::end_data_table_row();
+    $Str .= &Apache::loncommon::end_data_table();
+    #
+    $Str .= '</p>';
     $Str .= '<input type="submit" name="GenerateStatistics" value="'.
         &mt('Generate Statistics').'" />';
-    $Str .= '&nbsp;'x5;
-    $Str .= '<input type="submit" name="ClearCache" value="'.
-        &mt('Clear Caches').'" />';
-    $Str .= '&nbsp;'x5;
-    return ($Str,$outputmode,$show);
+    $Str .= ('&nbsp;'x10);
+    #
+    return $Str;
 }
 
 ###############################################
@@ -266,14 +672,26 @@ Main interface to problem statistics.
 
 ###############################################
 ###############################################
+my $navmap;
+my @sequences;
+
+sub clean_up {
+    undef($navmap);
+    undef(@sequences);
+}
+
 sub BuildProblemStatisticsPage {
     my ($r,$c)=@_;
+    undef($navmap);
+    undef(@sequences);
     #
     my %Saveable_Parameters = ('Status' => 'scalar',
                                'statsoutputmode' => 'scalar',
                                'Section' => 'array',
+                               'Groups' => 'array',
                                'StudentData' => 'array',
-                               'Maps' => 'array');
+                               'Maps' => 'array',
+                               'fieldselections'=> 'array');
     &Apache::loncommon::store_course_settings('statistics',
                                               \%Saveable_Parameters);
     &Apache::loncommon::restore_course_settings('statistics',
@@ -281,342 +699,719 @@ sub BuildProblemStatisticsPage {
     #
     &Apache::lonstatistics::PrepareClasslist();
     #
-    my ($interface,$output_mode,$show) = &CreateInterface();
+    # Clear the package variables
+    undef(@StatsArray);
+    undef(%SeqStat);
+    #
+    # Finally let the user know we are here
+    $r->print(&Apache::lonhtmlcommon::breadcrumbs('Overall Problem Statistics',
+                                                'Statistics_Overall_Key'));
+
+    my $interface = &CreateInterface($r);
     $r->print($interface);
-    $r->print('<input type="hidden" name="statsfirstcall" value="no" />');
-    $r->print('<input type="hidden" name="sortby" value="'.$ENV{'form.sortby'}.
+    $r->print('<input type="hidden" name="sortby" value="'.$env{'form.sortby'}.
               '" />');
-    $r->print('<input type="hidden" name="plot" value="" />');
-    if (! exists($ENV{'form.statsfirstcall'})) {
+    #
+    my @CacheButtonHTML =
+        &Apache::lonstathelpers::manage_caches($r,'Statistics','stats_status');
+    my $Str;
+    foreach my $html (@CacheButtonHTML) {
+        $Str.=$html.('&nbsp;'x5);
+    }
+    #
+    $r->print($Str);
+    if (! exists($env{'form.firstrun'})) {
+        $r->print('<p class="LC_info"><b>'.
+                  &mt('Press "Generate Statistics" when you are ready.').
+                  '</b></p>'.
+                  '<p class="LC_info">'.
+                  &mt('It may take some time to update the student data '.
+                      'for the first analysis. Future analysis this session '.
+                      'will not have this delay.').
+                  '</p>');
+	&clean_up();
         return;
     }
+    $r->rflush();
     #
-    &Apache::lonstatistics::Gather_Student_Data($r);
-    #
-    #
-    if ($output_mode eq 'html') {
-        $r->print("<h2>".
-                  $ENV{'course.'.$ENV{'request.course.id'}.'.description'}.
-                  "</h2>\n");
-        $r->print("<h3>".localtime(time)."</h3>");
-        $r->rflush();
-        if ($show eq 'grouped') {
-            &output_html_grouped_by_sequence($r);
-        } elsif ($show eq 'ungrouped') {
-            &output_html_ungrouped($r);
-        }
-    } elsif ($output_mode eq 'excel') {
-        $r->print('<h2>'.&mt('Preparing Excel Spreadsheet').'</h2>');
-        &output_excel($r);
+    # This probably does not need to be done each time we are called, but
+    # it does not slow things down noticably.
+    &Apache::loncoursedata::populate_weight_table();
+    #
+    ($navmap,@sequences) =
+        &Apache::lonstatistics::selected_sequences_with_assessments();
+    if (! ref($navmap)) {
+        $r->print('<div class="LC_error">'.&mt('A course-wide error occurred.').'</div>'.
+                  '<h3>'.$navmap.'</h3>');
+	&clean_up();
+        return;
+    }
+    if (exists($env{'form.Excel'})) {
+        $r->print('<p>'.
+                  &Apache::lonstatistics::section_and_enrollment_description().
+                  '</p>');
+        &Excel_output($r);
     } else {
-        $r->print('<h1>'.&mt('Not implemented').'</h1>');
+        $r->print('<input type="submit" name="Excel" value="'.
+                  &mt('Produce Excel Output').'" />'.'&nbsp;'x5);
+        $r->rflush();
+        $r->print('<p>'.
+                  &Apache::lonstatistics::section_and_enrollment_description().
+                  '</p>');
+        my $count = 0;
+        foreach my $seq (@sequences) {
+            my @resources =
+                &Apache::lonstathelpers::get_resources($navmap,$seq);
+            $count += scalar(@resources);
+        }
+        if ($count > 10) {
+            $r->print('<p>'.
+                      &mt('Compiling statistics for [quant,_1,problem]',$count).
+                      '</p>');
+            if ($count > 30) {
+                $r->print('<p class="LC_info">'.&mt('This will take some time.').'</p>');
+            }
+            $r->rflush();
+        }
+        #
+        my $sortby = $env{'form.sortby'};
+        $sortby = 'container' if (! defined($sortby) || $sortby =~ /^\s*$/);
+        my $plot = $env{'form.plot'};
+        if ($plot eq '' || $plot eq 'none') {
+            undef($plot);
+        }
+        if ($sortby eq 'container' && ! defined($plot)) {
+            &output_sequence_statistics($r);
+            &output_html_by_sequence($r);
+        } else {
+            if (defined($plot)) {
+                &make_plot($r,$plot);
+            }
+            &output_html_stats($r);
+            &output_sequence_statistics($r);
+        }
     }
+    &clean_up();
     return;
 }
 
-###############################################
-###############################################
+sub output_sequence_statistics {
+    my ($r) = @_;
+    my $c=$r->connection();
+    $r->print('<h2>'.&mt('Sequence Statistics').
+	      &Apache::loncommon::help_open_topic('Statistics_Sequence').
+	      '</h2>');
+    $r->print(&Apache::loncommon::start_data_table().&Apache::loncommon::start_data_table_header_row());
+    $r->print(&sequence_html_header());
+    $r->print(&Apache::loncommon::end_data_table_header_row());
+    foreach my $seq (@sequences) {
+        last if ($c->aborted);
+        &compute_sequence_statistics($seq);
+        $r->print(&sequence_html_output($seq));
+    }
+    $r->print(&Apache::loncommon::end_data_table());
+    $r->rflush();
+    return;
+}
 
-=pod 
 
-=item &output_html_grouped_by_sequence()
+##########################################################
+##########################################################
+##
+## HTML output routines
+##
+##########################################################
+##########################################################
+sub output_html_by_sequence {
+    my ($r) = @_;
+    my $c = $r->connection();
+    $r->print('<br>'.&html_preamble());
+    #
+    foreach my $seq (@sequences) {
+        last if ($c->aborted);
+        $r->print("<h3>".$seq->compTitle."</h3>".
+                    &Apache::loncommon::start_data_table().
+                    &Apache::loncommon::start_data_table_header_row().
+                    &statistics_table_header('no container').
+                    &Apache::loncommon::end_data_table_header_row()."\n");
+        my @Data = &compute_statistics_on_sequence($seq);
+        foreach my $data (@Data) {
+            $r->print(&Apache::loncommon::start_data_table_row().
+                    &statistics_html_table_data($data,'no container').
+                    &Apache::loncommon::end_data_table_row()."\n");
+        }
+        $r->print(&Apache::loncommon::end_data_table()."\n");
+        $r->rflush();
+    }
+    return;
+}
+
+sub output_html_stats {
+    my ($r)=@_;
+    &compute_all_statistics($r);
+    $r->print(&html_preamble());
+    &sort_data($env{'form.sortby'});
+    #
+    my $count=0;
+    foreach my $data (@StatsArray) {
+        if ($count++ % 50 == 0) {
+            $r->print(&Apache::loncommon::end_data_table());
+            $r->print(&Apache::loncommon::start_data_table().
+                    &Apache::loncommon::start_data_table_row().
+                    &statistics_table_header().
+                    &Apache::loncommon::end_data_table_row());
+        }
+        $r->print(&Apache::loncommon::start_data_table_row().
+                &statistics_html_table_data($data).
+                &Apache::loncommon::end_data_table_row());
+    }
+    $r->print(&Apache::loncommon::end_data_table_row());
+    return;
+}
 
-Presents the statistics data as an html table organized by the order
-the assessments appear in the course.
+sub html_preamble {
+    my $Str='';
+    $Str .= "<h2>".
+        $env{'course.'.$env{'request.course.id'}.'.description'}.
+        "</h2>\n";
+    my ($starttime,$endtime) = &Apache::lonstathelpers::get_time_limits();
+    if (defined($starttime) || defined($endtime)) {
+        # Inform the user what the time limits on the data are.
+        $Str .= '<h3>'.&mt('Statistics on submissions from [_1] to [_2]',
+                           &Apache::lonlocal::locallocaltime($starttime),
+                           &Apache::lonlocal::locallocaltime($endtime)
+                           ).'</h3>';
+    }
+    $Str .= "<p>".&mt('Compiled on [_1]',
+                       &Apache::lonlocal::locallocaltime(time))."</p>";
+    return $Str;
+}
 
-=cut
 
 ###############################################
 ###############################################
-sub output_html_grouped_by_sequence {
-    my ($r) = @_;
-    my $problem_num = 0;
-    #$r->print(&ProblemStatisticsLegend());
-    foreach my $sequence (&Apache::lonstatistics::Sequences_with_Assess()) {
-        next if ($sequence->{'num_assess'}<1);
-        $r->print("<h3>".$sequence->{'title'}."</h3>");
-        $r->print('<table border="0"><tr><td bgcolor="#777777">'."\n");
-        $r->print('<table border="0" cellpadding="3">'."\n");
-        $r->print('<tr bgcolor="#FFFFE6">');
-        my $Str = &statistics_table_header('no container no plots');
-        $r->print('<tr bgcolor="#FFFFE6">'.$Str."</tr>\n");
-        foreach my $resource (@{$sequence->{'contents'}}) {
-            next if ($resource->{'type'} ne 'assessment');
-            foreach my $part (@{$resource->{'parts'}}) {
-                $problem_num++;
-                my $data = &get_statistics($sequence,$resource,$part,
-                                           $problem_num);
-                my $option = '';
-                $r->print('<tr>'.&statistics_html_table_data($data,
-                                                             'no container').
-                          "</tr>\n");
+##
+## Misc HTML output routines
+##
+###############################################
+###############################################
+sub statistics_html_table_data {
+    my ($data,$options) = @_;
+    my $row = '';
+    foreach my $field (@Fields) {
+        next if ($options =~ /no $field->{'name'}/);
+        next if ($field->{'selected'} ne 'yes');
+        $row .= '<td style="background-color:'.$field->{'color'}.'"';
+        if (exists($field->{'align'})) {
+            $row .= ' align="'.$field->{'align'}.'"';
             }
+        $row .= '>';
+        if (exists($field->{'special'}) && $field->{'special'} eq 'link') {
+            $row .= '<a href="'.$data->{$field->{'name'}.'.link'}.'">';
         }
-        $r->print("</table>\n");
-        $r->print("</td></tr></table>\n");
-        $r->rflush();
+        if (exists($field->{'format'}) && $data->{$field->{'name'}} !~ /[A-Z]/i) {
+            $row .= sprintf($field->{'format'},$data->{$field->{'name'}});
+        } else {
+            $row .= $data->{$field->{'name'}};
+        }
+        if (exists($field->{'special'}) && $field->{'special'} eq 'link') {
+            $row.= '</a>';
+        }
+        $row .= '</td>';
     }
-    #
-    return;
+    return $row;
 }
 
-###############################################
-###############################################
+sub statistics_table_header {
+    my ($options) = @_;
+    my $header_row;
+    foreach my $field (@Fields) {
+        next if ($options =~ /no $field->{'name'}/);
+        next if ($field->{'selected'} ne 'yes');
+        $header_row .= '<th>';
+        if (exists($field->{'sortable'}) && $field->{'sortable'} eq 'yes') {
+            $header_row .= '<a href="javascript:'.
+                'document.Statistics.sortby.value='."'".$field->{'name'}."'".
+                    ';document.Statistics.submit();">';
+        }
+        $header_row .= &mt($field->{'title'});
+        if ($options =~ /sortable/) {
+            $header_row.= '</a>';
+        }
+        if ($options !~ /no plots/        && 
+            exists($field->{'graphable'}) && 
+            $field->{'graphable'} eq 'yes') {
+            $header_row.=' (';
+            $header_row .= '<a href="javascript:'.
+                "document.Statistics.plot.value='$field->{'name'}'".
+                    ';document.Statistics.submit();">';
+            $header_row .= &mt('plot').'</a>)';
+        }
+        $header_row .= '</th>';
+    }
+    return $header_row;
+}
 
-=pod 
+sub sequence_html_header {
+    my $Str .= '<tr>';
+    foreach my $field (@SeqFields) {
+#        next if ($field->{'selected'} ne 'yes');
+        $Str .= '<th bgcolor="'.$field->{'color'}.'"';
+        $Str .= '>'.$field->{'title'}.'</th>';
+    }
+    $Str .= '</tr>';
+    return $Str;
+}
 
-=item &output_html_ungrouped()
 
-Presents the statistics data in a single html table which can be sorted by
-different columns.
+sub sequence_html_output {
+    my ($seq) = @_;
+    my $data = $SeqStat{$seq->symb};
+    my $row = '<tr>';
+    foreach my $field (@SeqFields) {
+        next if ($field->{'selected'} ne 'yes');
+        $row .= '<td bgcolor="'.$field->{'color'}.'"';
+        if (exists($field->{'align'})) {
+            $row .= ' align="'.$field->{'align'}.'"';
+        }
+        $row .= '>';
+        if (exists($field->{'format'})) {
+            $row .= sprintf($field->{'format'},$data->{$field->{'name'}});
+        } else {
+            $row .= $data->{$field->{'name'}};
+        }
+        $row .= '</td>';
+    }
+    $row .= '</tr>'."\n";
+    return $row;
+}
 
-=cut
+####################################################
+####################################################
+##
+##    Plotting Routines
+##
+####################################################
+####################################################
+sub make_plot {
+    my ($r,$plot) = @_;
+    &compute_all_statistics($r);
+    &sort_data($env{'form.sortby'});
+    if ($plot eq 'degrees') {
+        &degrees_plot($r);
+    } elsif ($plot eq 'tries statistics') {
+        &tries_data_plot($r);
+    } else {
+        &make_single_stat_plot($r,$plot);
+    }
+    return;
+}
 
-###############################################
-###############################################
-sub output_html_ungrouped {
-    my ($r,$option) = @_;
+sub make_single_stat_plot {
+    my ($r,$datafield) = @_;
     #
-    if (exists($ENV{'form.plot'}) && $ENV{'form.plot'} ne '') {
-        &plot_statistics($r,$ENV{'form.plot'});
+    my $title; my $yaxis;
+    foreach my $field (@Fields) {
+        next if ($field->{'name'} ne $datafield);
+        $title = &mt($field->{'long_title'});
+        $yaxis = &mt($field->{'title'});
+        last;
+    }
+    if ($title eq '' || $yaxis eq '') {
+        # datafield is something we do not know enough about to plot
+        $r->print('<p class="LC_warning">'.
+                  &mt('Unable to plot the requested statistic.').
+                  '</p>');
+        return;
     }
     #
-    my $problem_num = 0;
-    my $show_container = 0;
-    my $show_part = 0;
-    #$r->print(&ProblemStatisticsLegend());
-    my $sortby = undef;
-    foreach my $field (@Fields) {
-        if ($ENV{'form.sortby'} eq $field->{'name'}) {
-            $sortby = $field->{'name'};
+    # Build up the data sets to plot
+    my @Labels;
+    my @Data;
+    my $max = 1;
+    foreach my $data (@StatsArray) {
+        push(@Labels,$data->{'problem_num'});
+        push(@Data,$data->{$datafield});
+        if ($data->{$datafield}>$max) {
+            $max = $data->{$datafield};
+        }
+    }
+    foreach (1,2,3,4,5,10,15,20,25,40,50,75,100,150,200,250,300,500,600,750,
+             1000,1500,2000,2500,3000,3500,4000,5000,7500,10000,15000,20000) {
+        if ($max <= $_) {
+            $max = $_;
+            last;
         }
     }
-    if (! defined($sortby) || $sortby eq '' || $sortby eq 'problem_num') {
-        $sortby = 'container';
+    if ($max > 20000) {
+        $max = 10000*(int($max/10000)+1);
     }
-    # If there is more than one sequence, list their titles
-    my @Sequences = &Apache::lonstatistics::Sequences_with_Assess();
-    if (@Sequences < 1) {
-        $option .= ' no container';
-    }
-    #
-    # Compile the data
-    my @Statsarray;
-    foreach my $sequence (@Sequences) {
-        next if ($sequence->{'num_assess'}<1);
-        foreach my $resource (@{$sequence->{'contents'}}) {
-            next if ($resource->{'type'} ne 'assessment');
-            foreach my $part (@{$resource->{'parts'}}) {
-                $problem_num++;
-                my $data = &get_statistics($sequence,$resource,$part,
-                                           $problem_num);
-                $show_part = 1 if ($part ne '0');
-                #
-                push (@Statsarray,$data);
-            }
+    #
+    $r->print("<p>".&Apache::loncommon::DrawBarGraph($title,
+                                                     &mt('Problem Number'),
+                                                     $yaxis,
+                                                     $max,
+                                                     undef, # colors
+                                                     \@Labels,
+                                                     \@Data)."</p>\n");
+    return;
+}
+
+sub degrees_plot {
+    my ($r)=@_;
+    my $count = scalar(@StatsArray);
+    my $width = 50 + 10*$count;
+    $width = 300 if ($width < 300);
+    my $height = 300;
+    my $plot = '';
+    my $ymax = 0;
+    my $ymin = 0;
+    my @Disc; my @Diff; my @Labels;
+    foreach my $data (@StatsArray) {
+        push(@Labels,$data->{'problem_num'});
+        my $disc = $data->{'deg_of_disc'};
+        my $diff = $data->{'deg_of_diff'};
+        push(@Disc,$disc);
+        push(@Diff,$diff);
+        #
+        $ymin = $disc if ($ymin > $disc);
+        $ymin = $diff if ($ymin > $diff);
+        $ymax = $disc if ($ymax < $disc);
+        $ymax = $diff if ($ymax < $diff);
+    }
+    #
+    # Make sure we show relevant information.
+    if ($ymin < 0) {
+        if (abs($ymin) < 0.05) {
+            $ymin = 0;
+        } else {
+            $ymin = -1;
+        }
+    }
+    if ($ymax > 0) {
+        if (abs($ymax) < 0.05) {
+            $ymax = 0;
+        } else {
+            $ymax = 1;
         }
     }
     #
-    # Sort the data
-    my @OutputOrder;
-    if ($sortby eq 'container') {
-        @OutputOrder = @Statsarray;
+    my $xmax = $Labels[-1];
+    if ($xmax > 50) {
+        if ($xmax % 10 != 0) {
+            $xmax = 10 * (int($xmax/10)+1);
+        }
     } else {
-        # $sortby is already defined, so we can charge ahead
-        if ($sortby =~ /^(title|part)$/i) {
-            # Alpha comparison
-            @OutputOrder = sort {
-                lc($a->{$sortby}) cmp lc($b->{$sortby}) ||
-                    lc($a->{'title'}) cmp lc($b->{'title'}) ||
-                        lc($a->{'part'}) cmp lc($b->{'part'});
-            } @Statsarray;
-        } else {
-            # Numerical comparison
-            @OutputOrder = sort {
-                my $retvalue = 0;
-                if ($b->{$sortby} eq 'nan') {
-                    if ($a->{$sortby} ne 'nan') {
-                        $retvalue = -1;
-                    } else {
-                        $retvalue = 0;
-                    }
-                }
-                if ($a->{$sortby} eq 'nan') {
-                    if ($b->{$sortby} ne 'nan') {
-                        $retvalue = 1;
-                    }
-                }
-                if ($retvalue eq '0') {
-                    $retvalue = $b->{$sortby} <=> $a->{$sortby} ||
-                                lc($a->{'title'}) <=> lc($b->{'title'}) ||
-                                lc($a->{'part'})  <=> lc($b->{'part'});
-                }
-                $retvalue;
-            } @Statsarray;
+        if ($xmax % 5 != 0) {
+            $xmax = 5 * (int($xmax/5)+1);
         }
     }
-    $option .= 'no part' if (! $show_part);
-    my $num_output = 0;
     #
-    # output the headers
-    $r->print('<table border="0"><tr><td bgcolor="#777777">'."\n");
-    $r->print('<table border="0" cellpadding="3">'."\n");
-    my $Str = &statistics_table_header($option.' sortable');
-    $r->print('<tr bgcolor="#FFFFE6">'.$Str."</tr>\n");
-    #
-    foreach my $rowdata (@OutputOrder) {
-        $num_output++;
-        if ($num_output % 25 == 0) {
-            $r->print("</table>\n</td></tr></table>\n");
-            #
-            $r->print('<table border="0"><tr><td bgcolor="#777777">'."\n");
-            $r->print('<table border="0" cellpadding="3">'."\n");
-            my $Str = &statistics_table_header($option.' sortable');
-            $r->print('<tr bgcolor="#FFFFE6">'.$Str."</tr>\n");
-            $r->rflush();
+    my $discdata .= '<data>'.join(',',@Labels).'</data>'.$/.
+                    '<data>'.join(',',@Disc).'</data>'.$/;
+    #
+    my $diffdata .= '<data>'.join(',',@Labels).'</data>'.$/.
+                    '<data>'.join(',',@Diff).'</data>'.$/;
+    #
+    my $title = &mt('Degree of Discrimination[_1]and Degree of Difficulty','\n');
+    if ($xmax > 50) {
+        $title = &mt('Degree of Discrimination and Degree of Difficulty');
+    }
+    my %lt = &Apache::lonlocal::texthash(
+        'alttag' => 'Degree of Discrimination and Degree of Difficulty Plot',
+        'xlabel' => 'Problem Number',
+    );
+    #
+    $plot=<<"END";
+<gnuplot 
+    texfont="10"
+    fgcolor="x000000"
+    plottype="Cartesian"
+    font="large"
+    grid="on"
+    align="center"
+    border="on"
+    transparent="on"
+    alttag="$lt{'alttag'}"
+    samples="100"
+    bgcolor="xffffff"
+    height="$height"
+    width="$width">
+    <key 
+        pos="top right"
+        title=""
+        box="off" />
+    <title>$title</title>
+    <axis xmin="0" ymin="$ymin" xmax="$xmax" ymax="$ymax" color="x000000" />
+    <xlabel>$lt{'xlabel'}</xlabel>
+    <curve 
+        linestyle="linespoints" 
+        name="DoDisc" 
+        pointtype="0" 
+        color="x000000">
+        $discdata
+    </curve>
+    <curve 
+        linestyle="linespoints" 
+        name="DoDiff" 
+        pointtype="0" 
+        color="xFF0000">
+        $diffdata
+    </curve>
+</gnuplot>
+END
+    my $plotresult =
+        '<p>'.&Apache::lonxml::xmlparse($r,'web',$plot).'</p>'.$/;
+    $r->print($plotresult);
+    return;
+}
+
+sub tries_data_plot {
+    my ($r)=@_;
+    my $count = scalar(@StatsArray);
+    my $width = 50 + 10*$count;
+    $width = 300 if ($width < 300);
+    my $height = 300;
+    my $plot = '';
+    my @STD;  my @Mean; my @Max; my @Min;
+    my @Labels;
+    my $ymax = 5;
+    foreach my $data (@StatsArray) {
+        my $max = $data->{'mean_tries'} + $data->{'std_tries'};
+        $ymax = $max if ($ymax < $max);
+        $ymax = $max if ($ymax < $max);
+        push(@Labels,$data->{'problem_num'});
+        push(@STD,$data->{'std_tries'});
+        push(@Mean,$data->{'mean_tries'});
+    }
+    #
+    # Make sure we show relevant information.
+    my $xmax = $Labels[-1];
+    if ($xmax > 50) {
+        if ($xmax % 10 != 0) {
+            $xmax = 10 * (int($xmax/10)+1);
+        }
+    } else {
+        if ($xmax % 5 != 0) {
+            $xmax = 5 * (int($xmax/5)+1);
         }
-        $r->print('<tr>'.&statistics_html_table_data($rowdata,$option).
-                  "</tr>\n");
     }
-    $r->print("</table>\n");
-    $r->print("</td></tr></table>\n");
-    $r->rflush();
+    $ymax = int($ymax)+1+2;
     #
+    my $std_data .= '<data>'.join(',',@Labels).'</data>'.$/.
+                    '<data>'.join(',',@Mean).'</data>'.$/;
+    #
+    my $std_error_data .= '<data>'.join(',',@Labels).'</data>'.$/.
+                          '<data>'.join(',',@Mean).'</data>'.$/.
+                          '<data>'.join(',',@STD).'</data>'.$/;
+    #
+    my $title = &mt('Mean and S.D. of Tries');
+    if ($xmax > 30) {
+        $title = &mt('Mean and Standard Deviation of Tries');
+    }
+    #
+    my %lt = &Apache::lonlocal::texthash(
+        'alttag' => 'Mean and S.D of Tries Plot',
+        'xlabel' => 'Problem Number',
+        'ylabel' => 'Number of Tries',
+    );
+    $plot=<<"END";
+<gnuplot 
+    texfont="10"
+    fgcolor="x000000"
+    plottype="Cartesian"
+    font="large"
+    grid="on"
+    align="center"
+    border="on"
+    transparent="on"
+    alttag="$lt{'alttag'}"
+    samples="100"
+    bgcolor="xffffff"
+    height="$height"
+    width="$width">
+    <title>$title</title>
+    <axis xmin="0" ymin="0" xmax="$xmax" ymax="$ymax" color="x000000" />
+    <xlabel>$lt{'xlabel'}</xlabel>
+    <ylabel>$lt{'ylabel'}</ylabel>
+    <curve 
+        linestyle="yerrorbars"
+        name="S.D. Tries" 
+        pointtype="1" 
+        color="x666666">
+        $std_error_data
+    </curve>
+    <curve 
+        linestyle="points"
+        name="Mean Tries" 
+        pointtype="1" 
+        color="xCC4444">
+        $std_data
+    </curve>
+</gnuplot>
+END
+    my $plotresult =
+        '<p>'.&Apache::lonxml::xmlparse($r,'web',$plot).'</p>'.$/;
+    $r->print($plotresult);
     return;
 }
 
+sub plot_dropdown {
+    my $current = '';
+    my $title;
+    #
+    if (defined($env{'form.plot'})) {
+        $current = $env{'form.plot'};
+    }
+    #
+    my @Additional_Plots = (
+                            { graphable=>'yes',
+                              name => 'degrees',
+                              title => 'Difficulty Indexes' },
+                            { graphable=>'yes',
+                              name => 'tries statistics',
+                              title => 'Tries Statistics' });
+    #
+    my $Str= "\n".'<select name="plot" size="1">';
+    $Str .= '<option name="none"></option>'."\n";
+    $Str .= '<option name="none2">'.&mt('none').'</option>'."\n";
+    foreach my $field (@Additional_Plots,@Fields) {
+        if (! exists($field->{'graphable'}) ||
+            $field->{'graphable'} ne 'yes') {
+            next;
+        }
+        $Str .= '<option value="'.$field->{'name'}.'"';
+        if ($field->{'name'} eq $current) {
+            $Str .= ' selected="selected"';
+        }
+        $title = &mt($field->{'long_title'});
+        $title = &mt($field->{'title'}) if (!$title);
+        $Str.= '>'.$title.'</option>'."\n";
+    }
+    $Str .= '</select>'."\n";
+    return $Str;
+}
+
 ###############################################
 ###############################################
-
-=pod 
-
-=item &output_excel()
-
-Presents the statistical data in an Excel 95 compatable spreadsheet file.
-
-=cut
-
+##
+## Excel output routines
+##
 ###############################################
 ###############################################
-sub output_excel {
+sub Excel_output {
     my ($r) = @_;
-    my $filename = '/prtspool/'.
-        $ENV{'user.name'}.'_'.$ENV{'user.domain'}.'_'.
-            time.'_'.rand(1000000000).'.xls';
-    #
-    my $excel_workbook = undef;
-    my $excel_sheet = undef;
-    #
-    my $rows_output = 0;
-    my $cols_output = 0;
-    #
-    # Create sheet
-    $excel_workbook = Spreadsheet::WriteExcel->new('/home/httpd'.$filename);
-    #
-    # Check for errors
-    if (! defined($excel_workbook)) {
-        $r->log_error("Error creating excel spreadsheet $filename: $!");
-        $r->print(&mt("Problems creating new Excel file.  ".
-                  "This error has been logged.  ".
-                  "Please alert your LON-CAPA administrator."));
-        return ;
-    }
-    #
-    # The excel spreadsheet stores temporary data in files, then put them
-    # together.  If needed we should be able to disable this (memory only).
-    # The temporary directory must be specified before calling 'addworksheet'.
-    # File::Temp is used to determine the temporary directory.
-    $excel_workbook->set_tempdir($Apache::lonnet::tmpdir);
+    $r->print('<h2>'.&mt('Preparing Excel Spreadsheet').'</h2>');
+    ##
+    ## Compute the statistics
+    &compute_all_statistics($r);
+    my $c = $r->connection;
+    return if ($c->aborted());
+    #
+    my ($starttime,$endtime) = &Apache::lonstathelpers::get_time_limits();
+    ##
+    ## Create the excel workbook
+    my ($excel_workbook,$filename,$format) =
+        &Apache::loncommon::create_workbook($r);
+    return if (! defined($excel_workbook));
     #
     # Add a worksheet
-    my $sheetname = $ENV{'course.'.$ENV{'request.course.id'}.'.description'};
+    my $sheetname = $env{'course.'.$env{'request.course.id'}.'.description'};
     if (length($sheetname) > 31) {
         $sheetname = substr($sheetname,0,31);
     }
-    $excel_sheet = $excel_workbook->addworksheet(
-                       &Apache::loncommon::clean_excel_name($sheetname)
-                                                 );
+    my $excel_sheet = $excel_workbook->addworksheet(
+        &Apache::loncommon::clean_excel_name($sheetname));
+    ##
+    ## Begin creating excel sheet
+    ##
+    my ($rows_output,$cols_output) = (0,0);
     #
     # Put the course description in the header
     $excel_sheet->write($rows_output,$cols_output++,
-                   $ENV{'course.'.$ENV{'request.course.id'}.'.description'});
+                   $env{'course.'.$env{'request.course.id'}.'.description'},
+                        $format->{'h1'});
     $cols_output += 3;
     #
     # Put a description of the sections listed
     my $sectionstring = '';
-    my @Sections = @Apache::lonstatistics::SelectedSections;
-    if (scalar(@Sections) > 1) {
-        if (scalar(@Sections) > 2) {
-            my $last = pop(@Sections);
-            $sectionstring = "Sections ".join(', ',@Sections).', and '.$last;
-        } else {
-            $sectionstring = "Sections ".join(' and ',@Sections);
-        }
-    } else {
-        if ($Sections[0] eq 'all') {
-            $sectionstring = "All sections";
-        } else {
-            $sectionstring = "Section ".$Sections[0];
-        }
+    $excel_sheet->write($rows_output,$cols_output++,
+                        &Apache::lonstatistics::section_and_enrollment_description('plaintext'),
+                        $format->{'h3'});
+    $cols_output += scalar(&Apache::lonstatistics::get_selected_sections());
+    $cols_output += scalar(&Apache::lonstatistics::get_selected_groups());
+    #
+    # Time restrictions
+    my $time_string;
+    if (defined($starttime)) {
+        # call localtime but not lonlocal:locallocaltime because excel probably
+        # cannot handle localized text.  Probably.
+        $time_string .= 'Data collected from '.localtime($time_string);
+        if (defined($endtime)) {
+            $time_string .= ' to '.localtime($endtime);
+        }
+        $time_string .= '.';
+    } elsif (defined($endtime)) {
+        # See note above about lonlocal:locallocaltime
+        $time_string .= 'Data collected before '.localtime($endtime).'.';
+    }
+    if (defined($time_string)) {
+        $excel_sheet->write($rows_output,$cols_output++,$time_string);
+        $cols_output+= 5;
     }
-    $excel_sheet->write($rows_output,$cols_output++,$sectionstring);
-    $cols_output += scalar(@Sections);
     #
     # Put the date in there too
     $excel_sheet->write($rows_output,$cols_output++,
                         'Compiled on '.localtime(time));
     #
-    $rows_output++; 
+    $rows_output++;
     $cols_output=0;
-    #
-    # Long Headersheaders
-    foreach my $field (@Fields) {
-        next if ($field->{'name'} eq 'problem_num');
-        if (exists($field->{'long_title'})) {
+    ##
+    ## Sequence Statistics
+    ##
+    &write_headers($excel_sheet,$format,\$rows_output,\$cols_output,
+                   \@SeqFields);
+    foreach my $seq (@sequences) {
+        my $data = $SeqStat{$seq->symb};
+        $cols_output=0;
+        foreach my $field (@SeqFields) {
+            next if ($field->{'selected'} ne 'yes');
+            my $fieldformat = undef;
+            if (exists($field->{'excel_format'})) {
+                $fieldformat = $format->{$field->{'excel_format'}};
+            }
             $excel_sheet->write($rows_output,$cols_output++,
-                                $field->{'long_title'});
-        } else {
-            $excel_sheet->write($rows_output,$cols_output++,'');
+                                $data->{$field->{'name'}},$fieldformat);
         }
+        $rows_output++;
+        $cols_output=0;
     }
+    ##
+    ## Resource Statistics
+    ##
     $rows_output++;
     $cols_output=0;
-    # Brief headers
-    foreach my $field (@Fields) {
-        next if ($field->{'name'} eq 'problem_num');
-        # Use english for excel as I am not sure how well excel handles 
-        # other character sets....
-        $excel_sheet->write($rows_output,$cols_output++,$field->{'title'});
-    }
-    $rows_output++;
+    &write_headers($excel_sheet,$format,\$rows_output,\$cols_output,
+                   \@Fields);
     #
-    # Write the data
-    my $problem_num=0;
-    foreach my $sequence (&Apache::lonstatistics::Sequences_with_Assess()) {
-        next if ($sequence->{'num_assess'}<1);
-        foreach my $resource (@{$sequence->{'contents'}}) {
-            next if ($resource->{'type'} ne 'assessment');
-            foreach my $part (@{$resource->{'parts'}}) {
-                $cols_output=0;
-                $problem_num++;
-                my $data = &get_statistics($sequence,$resource,$part,
-                                           $problem_num);
-                #
-                if (!defined($part) || $part eq '') {
-                    $part = ' ';
-                }
-                foreach my $field (@Fields) {
-                    next if ($field->{'name'} eq 'problem_num');
-                    $excel_sheet->write($rows_output,$cols_output++,
-                                        $data->{$field->{'name'}});
-                }
-                $rows_output++;
+    foreach my $data (@StatsArray) {
+        $cols_output=0;
+        foreach my $field (@Fields) {
+            next if ($field->{'selected'} ne 'yes');
+            next if ($field->{'name'} eq 'problem_num');
+            my $fieldformat = undef;
+            if (exists($field->{'excel_format'})) {
+                $fieldformat = $format->{$field->{'excel_format'}};
             }
+            $excel_sheet->write($rows_output,$cols_output++,
+                                $data->{$field->{'name'}},$fieldformat);
         }
+        $rows_output++;
+        $cols_output=0;
     }
     #
-    # Write the excel file
     $excel_workbook->close();
+    #
     # Tell the user where to get their excel file
     $r->print('<br />'.
               '<a href="'.$filename.'">'.
@@ -625,254 +1420,410 @@ sub output_excel {
     return;
 }
 
-###############################################
-###############################################
-
-=pod 
-
-=item &statistics_html_table_data()
-
-Help function used to format the rows for HTML table output.
-
-=cut
-
-###############################################
-###############################################
-sub statistics_html_table_data {
-    my ($data,$options) = @_;
-    my $row = '';
-    foreach my $field (@Fields) {
-        next if ($options =~ /no $field->{'name'}/);
-        $row .= '<td bgcolor="'.$field->{'color'}.'"';
-        if (exists($field->{'align'})) {
-            $row .= ' align="'.$field->{'align'}.'"';
-            }
-        $row .= '>';
-        if (exists($field->{'special'}) && $field->{'special'} eq 'link') {
-            $row .= '<a href="'.$data->{$field->{'name'}.'.link'}.'">';
-        }
-        if (exists($field->{'format'})) {
-            $row .= sprintf($field->{'format'},$data->{$field->{'name'}});
+##
+## &write_headers
+##
+sub write_headers {
+    my ($excel_sheet,$format,$rows_output,$cols_output,$Fields) = @_;
+    ##
+    ## First the long titles
+    foreach my $field (@{$Fields}) {
+        next if ($field->{'name'} eq 'problem_num');
+        next if ($field->{'selected'} ne 'yes');
+        if (exists($field->{'long_title'})) {
+            $excel_sheet->write($$rows_output,${$cols_output},
+                                $field->{'long_title'},
+                                $format->{'bold'});
         } else {
-            $row .= $data->{$field->{'name'}};
+            $excel_sheet->write($$rows_output,${$cols_output},'');
         }
-        if (exists($field->{'special'}) && $field->{'special'} eq 'link') {
-            $row.= '</a>';
-        }
-        $row .= '</td>';
+        ${$cols_output}+= 1;
     }
-    return $row;
+    ${$cols_output} =0;
+    ${$rows_output}+=1;
+    ##
+    ## Then the short titles
+    foreach my $field (@{$Fields}) {
+        next if ($field->{'selected'} ne 'yes');
+        next if ($field->{'name'} eq 'problem_num');
+        # Use english for excel as I am not sure how well excel handles
+        # other character sets....
+        $excel_sheet->write($$rows_output,$$cols_output,
+                            $field->{'title'},
+                            $format->{'bold'});
+        $$cols_output+=1;
+    }
+    ${$cols_output} =0;
+    ${$rows_output}+=1;
+    return;
 }
 
-sub statistics_table_header {
-    my ($options) = @_;
-    my $header_row;
-    foreach my $field (@Fields) {
-        next if ($options =~ /no $field->{'name'}/);
-        $header_row .= '<th>';
-        if ($options =~ /sortable/ && 
-            exists($field->{'sortable'}) && $field->{'sortable'} eq 'yes') {
-            $header_row .= '<a href="javascript:'.
-                'document.Statistics.sortby.value='."'".$field->{'name'}."'".
-                    ';document.Statistics.submit();">';
-        }
-        $header_row .= &mt($field->{'title'});
-        if ($options =~ /sortable/) {
-            $header_row.= '</a>';
-        }
-        if ($options !~ /no plots/        && 
-            exists($field->{'graphable'}) && 
-            $field->{'graphable'} eq 'yes') {
-            $header_row.=' (';
-            $header_row .= '<a href="javascript:'.
-                "document.Statistics.plot.value='$field->{'name'}'".
-                    ';document.Statistics.submit();">';
-            $header_row .= &mt('plot').'</a>)';
+##################################################
+##################################################
+##
+## Statistics Gathering and Manipulation Routines
+##
+##################################################
+##################################################
+sub compute_statistics_on_sequence {
+    my ($seq) = @_;
+    my @Data;
+    foreach my $res (&Apache::lonstathelpers::get_resources($navmap,$seq)) {
+        foreach my $part (@{$res->parts}) {
+            next if (($res->is_survey($part)) || ($res->is_anonsurvey($part))) ;
+            #
+            # This is where all the work happens
+            my $data = &get_statistics($seq,$res,$part,scalar(@StatsArray)+1);
+            push (@Data,$data);
+            push (@StatsArray,$data);
         }
-        $header_row .= '</th>';
     }
-    return $header_row;
+    return @Data;
 }
 
-###############################################
-###############################################
-
-=pod 
-
-=item &plot_statistics()
-
-=cut
+sub compute_all_statistics {
+    my ($r) = @_;
+    if (@StatsArray > 0) {
+        # Assume we have already computed the statistics
+        return;
+    }
+    my $c = $r->connection;
+    foreach my $seq (@sequences) {
+        last if ($c->aborted);
+        &compute_sequence_statistics($seq);
+        &compute_statistics_on_sequence($seq);
+    }
+}
 
-###############################################
-###############################################
-sub plot_statistics {
-    my ($r,$datafield) = @_;
-    my @Data;
-    #
+sub sort_data {
+    my ($sortkey) = @_;
+    return if (! @StatsArray);
     #
-    my $sortfield = undef;
-    my $title = undef;
+    # Sort the data
+    my $sortby = undef;
     foreach my $field (@Fields) {
-        if ($datafield eq $field->{'name'} &&
-            exists($field->{'graphable'}) && $field->{'graphable'} eq 'yes') {
-            $sortfield = $field->{'name'};
-            $title = $field->{'long_title'};
-        }
-    }
-    return if (! defined($sortfield) || $sortfield eq '');
-    #
-    my $Max = 0;
-    my $problem_num = 0;
-    foreach my $sequence (&Apache::lonstatistics::Sequences_with_Assess()) {
-        next if ($sequence->{'num_assess'}<1);
-        foreach my $resource (@{$sequence->{'contents'}}) {
-            next if ($resource->{'type'} ne 'assessment');
-            foreach my $part (@{$resource->{'parts'}}) {
-                my $problem_number++;
-                my $data = &get_statistics($sequence,$resource,$part,
-                                           $problem_num);
-                my $value = $data->{$sortfield};
-                $Max = $value if ($Max < $value);
-                push (@Data,$value);
-            }
+        if ($sortkey eq $field->{'name'}) {
+            $sortby = $field->{'name'};
         }
     }
-    #
-    # Print out plot request
-    my $yaxis = '';
-    if ($sortfield eq 'per_wrong') {
-        $yaxis = 'Percent';
-    }
-    #
-    # Determine appropriate value for $Max
-    if ($sortfield eq 'deg_of_diff') {
-        if ($Max > 0.5) {
-            $Max = 1;
-        } elsif ($Max > 0.2) {
-            $Max = 0.5;
-        } elsif ($Max > 0.1) {
-            $Max = 0.2;
-        }
-    } elsif ($sortfield eq 'per_wrong') {
-        if ($Max > 50) {
-            $Max = 100;
-        } elsif ($Max > 25) {
-            $Max = 50;
-        } elsif ($Max > 20) {
-            $Max = 25;
-        } elsif ($Max > 10) {
-            $Max = 20;
-        } elsif ($Max > 5) {
-            $Max = 10;
+    if (! defined($sortby) || $sortby eq '' || $sortby eq 'problem_num') {
+        $sortby = 'container';
+    }
+    if ($sortby ne 'container') {
+        # $sortby is already defined, so we can charge ahead
+        if ($sortby =~ /^(title|part)$/i) {
+            # Alpha comparison
+            @StatsArray = sort {
+                lc($a->{$sortby}) cmp lc($b->{$sortby}) ||
+                lc($a->{'title'}) cmp lc($b->{'title'}) ||
+                lc($a->{'part'}) cmp lc($b->{'part'});
+            } @StatsArray;
         } else {
-            $Max = 5;
+            # Numerical comparison
+            @StatsArray = sort {
+                my $retvalue = 0;
+                if ($b->{$sortby} eq 'nan') {
+                    if ($a->{$sortby} ne 'nan') {
+                        $retvalue = -1;
+                    } else {
+                        $retvalue = 0;
+                    }
+                }
+                if ($a->{$sortby} eq 'nan') {
+                    if ($b->{$sortby} ne 'nan') {
+                        $retvalue = 1;
+                    }
+                }
+                if ($retvalue eq '0') {
+                    $retvalue = $b->{$sortby} <=> $a->{$sortby}     ||
+                            lc($a->{'title'}) <=> lc($b->{'title'}) ||
+                            lc($a->{'part'})  <=> lc($b->{'part'});
+                }
+                $retvalue;
+            } @StatsArray;
         }
     }
-    
-    $r->print("<p>".&Apache::loncommon::DrawBarGraph($title,
-                                                     'Problem Number',
-                                                     $yaxis,
-                                                     $Max,
-                                                     undef,
-                                                     \@Data)."</p>\n");
     #
-    # Print out the data
-    $ENV{'form.sortby'} = 'Contents';
-#    &output_html_ungrouped($r);
+    # Renumber the data set
+    my $count;
+    foreach my $data (@StatsArray) {
+        $data->{'problem_num'} = ++$count;
+    }
     return;
 }
 
+########################################################
+########################################################
+
+=pod
+
+=item &get_statistics()
+
+Wrapper routine from the call to loncoursedata::get_problem_statistics.
+Calls lonstathelpers::get_time_limits() to limit the data set by time
+and &compute_discrimination_factor
+
+Inputs: $sequence, $resource, $part, $problem_num
+
+Returns: Hash reference with statistics data from
+loncoursedata::get_problem_statistics.
+
+=cut
+
+########################################################
+########################################################
 sub get_statistics {
     my ($sequence,$resource,$part,$problem_num) = @_;
     #
-    my $symb = $resource->{'symb'};
-    my $courseid = $ENV{'request.course.id'};
+    my ($starttime,$endtime) = &Apache::lonstathelpers::get_time_limits();
+    my $symb = $resource->symb;
+    my $courseid = $env{'request.course.id'};
     #
-    my $students = \@Apache::lonstatistics::Students;
-    if ($Apache::lonstatistics::SelectedSections[0] eq 'all') {
-        $students = undef;
-    }
     my $data = &Apache::loncoursedata::get_problem_statistics
-                        ($students,$symb,$part,$courseid);
+                        ([&Apache::lonstatistics::get_selected_sections()],
+                         [&Apache::lonstatistics::get_selected_groups()],
+                         $Apache::lonstatistics::enrollment_status,
+                         $symb,$part,$courseid,$starttime,$endtime);
+    $data->{'symb'}        = $symb;
     $data->{'part'}        = $part;
     $data->{'problem_num'} = $problem_num;
-    $data->{'container'}   = $sequence->{'title'};
-    $data->{'title'}       = $resource->{'title'};
-    $data->{'title.link'}  = $resource->{'src'}.'?symb='.
-        &Apache::lonnet::escape($resource->{'symb'});
-    #
+    $data->{'container'}   = $sequence->compTitle;
+    $data->{'title'}       = $resource->compTitle;
+    $data->{'title.link'}  = $resource->src.'?symb='.
+        &escape($resource->symb);
+    #
+    if ($SelectedFields{'deg_of_disc'}) {
+        $data->{'deg_of_disc'} =
+            &compute_discrimination_factor($resource,$part,$sequence);
+    }
+    #
+    # Store in metadata if computations were done for all students
+    if ($data->{'num_students'} > 1) {
+        my @Sections = &Apache::lonstatistics::get_selected_sections();
+        my $sections = '"'.join(' ',@Sections).'"';
+        $sections =~ s/&+/_/g;  # Ensure no special characters
+        $data->{'sections'}=$sections;
+        $data->{'course'} = $env{'request.course.id'};
+        my $urlres=(&Apache::lonnet::decode_symb($resource->symb))[2];
+        my %storestats =
+            &LONCAPA::lonmetadata::dynamic_metadata_storage($data);
+        my ($dom,$user) = ($urlres=~m{^($LONCAPA::domain_re)/($LONCAPA::username_re)});
+        &Apache::lonnet::put('nohist_resevaldata',\%storestats,$dom,$user);
+    }
+    #
+    $data->{'tries_per_correct'} = $data->{'tries'} / 
+        ($data->{'num_solved'}+0.1);
+    #
+    # Get the due date for research purposes (commented out most of the time)
+#    my $duedate = &Apache::lonnet::EXT('resource.'.$part.'.duedate',$symb);;
+#    my $opendate = &Apache::lonnet::EXT('resource.'.$part.'.opendate',$symb);
+#    my $maxtries = &Apache::lonnet::EXT('resource.'.$part.'.maxtries',$symb);
+#    my $hinttries = &Apache::lonnet::EXT('resource.'.$part.'.hinttries',$symb);
+    my $weight = &Apache::lonnet::EXT('resource.'.$part.'.weight',$symb);
+    $data->{'weight'} = $weight;
+#    $data->{'duedate'} = $duedate;
+#    $data->{'opendate'} = $opendate;
+#    $data->{'maxtries'} = $maxtries;
+#    $data->{'hinttries'} = $hinttries;
+#    $data->{'resptypes'} = join(',',@{$resource->{'partdata'}->{$part}->{'ResponseTypes'}});
     return $data;
 }
 
 ###############################################
 ###############################################
 
-=pod 
+=pod
 
-=item &ProblemStatisticsLegend()
+=item &compute_discrimination_factor()
 
-HELP  This needs to be localized, or at least generated automatically.
+Inputs: $Resource, $Sequence
+
+Returns: integer between -1 and 1
 
 =cut
 
 ###############################################
 ###############################################
-sub ProblemStatisticsLegend {
-    my $Ptr = '';
-    $Ptr = '<table border="0">';
-    $Ptr .= '<tr><td>';
-    $Ptr .= '<b>#Stdnts</b></td>';
-    $Ptr .= '<td>Total number of students attempted the problem.';
-    $Ptr .= '</td></tr><tr><td>';
-    $Ptr .= '<b>Tries</b></td>';
-    $Ptr .= '<td>Total number of tries for solving the problem.';
-    $Ptr .= '</td></tr><tr><td>';
-    $Ptr .= '<b>Max Tries</b></td>';
-    $Ptr .= '<td>Largest number of tries for solving the problem by a student.';
-    $Ptr .= '</td></tr><tr><td>';
-    $Ptr .= '<b>Mean</b></td>';
-    $Ptr .= '<td>Average number of tries. [ Tries / #Stdnts ]';
-    $Ptr .= '</td></tr><tr><td>';
-    $Ptr .= '<b>#YES</b></td>';
-    $Ptr .= '<td>Number of students solved the problem correctly.';
-    $Ptr .= '</td></tr><tr><td>';
-    $Ptr .= '<b>#yes</b></td>';
-    $Ptr .= '<td>Number of students solved the problem by override.';
-    $Ptr .= '</td></tr><tr><td>';
-    $Ptr .= '<b>%Wrong</b></td>';
-    $Ptr .= '<td>Percentage of students who tried to solve the problem ';
-    $Ptr .= 'but is still incorrect. [ 100*((#Stdnts-(#YES+#yes))/#Stdnts) ]';
-    $Ptr .= '</td></tr><tr><td>';
-    $Ptr .= '<b>DoDiff</b></td>';
-    $Ptr .= '<td>Degree of Difficulty of the problem.  ';
-    $Ptr .= '[ 1 - ((#YES+#yes) / Tries) ]';
-    $Ptr .= '</td></tr><tr><td>';
-    $Ptr .= '<b>S.D.</b></td>';
-    $Ptr .= '<td>Standard Deviation of the tries.  ';
-    $Ptr .= '[ sqrt(sum((Xi - Mean)^2)) / (#Stdnts-1) ';
-    $Ptr .= 'where Xi denotes every student\'s tries ]';
-    $Ptr .= '</td></tr><tr><td>';
-    $Ptr .= '<b>Skew.</b></td>';
-    $Ptr .= '<td>Skewness of the students tries.';
-    $Ptr .= '[(sqrt( sum((Xi - Mean)^3) / #Stdnts)) / (S.D.^3)]';
-    $Ptr .= '</td></tr><tr><td>';
-    $Ptr .= '<b>Dis.F.</b></td>';
-    $Ptr .= '<td>Discrimination Factor: A Standard for evaluating the ';
-    $Ptr .= 'problem according to a Criterion<br>';
-    $Ptr .= '<b>[Criterion to group students into %27 Upper Students - ';
-    $Ptr .= 'and %27 Lower Students]</b><br>';
-    $Ptr .= '<b>1st Criterion</b> for Sorting the Students: ';
-    $Ptr .= '<b>Sum of Partial Credit Awarded / Total Number of Tries</b><br>';
-    $Ptr .= '<b>2nd Criterion</b> for Sorting the Students: ';
-    $Ptr .= '<b>Total number of Correct Answers / Total Number of Tries</b>';
-    $Ptr .= '</td></tr>';
-    $Ptr .= '<tr><td><b>Disc.</b></td>';
-    $Ptr .= '<td>Number of Students had at least one discussion.';
-    $Ptr .= '</td></tr></table>';
-    return $Ptr;
+sub compute_discrimination_factor {
+    my ($resource,$part,$seq) = @_;
+    my $symb = $resource->symb;
+    my @Resources;
+    foreach my $res (&Apache::lonstathelpers::get_resources($navmap,$seq)){
+        next if ($res->symb eq $symb);
+        push (@Resources,$res->symb);
+    }
+    #
+    # rank
+    my ($starttime,$endtime) = &Apache::lonstathelpers::get_time_limits();
+    my $ranking =
+        &Apache::loncoursedata::rank_students_by_scores_on_resources
+        (\@Resources,
+         [&Apache::lonstatistics::get_selected_sections()],
+         [&Apache::lonstatistics::get_selected_groups()],
+         $Apache::lonstatistics::enrollment_status,undef,
+         $starttime,$endtime, $symb);
+    #
+    # compute their percent scores on the problems in the sequence,
+    my $number_to_grab = int(scalar(@{$ranking})/4);
+    my $num_students = scalar(@{$ranking});
+    my @BottomSet = map { $_->[&Apache::loncoursedata::RNK_student()];
+                      } @{$ranking}[0..$number_to_grab];
+    my @TopSet    =
+        map {
+            $_->[&Apache::loncoursedata::RNK_student()];
+          } @{$ranking}[-$number_to_grab..0];
+    if (! @BottomSet || (@BottomSet == 1 && $BottomSet[0] eq '') ||
+        ! @TopSet    || (@TopSet    == 1 && $TopSet[0]    eq '')) {
+        return 'nan';
+    }
+    my ($bottom_sum,$bottom_max) =
+        &Apache::loncoursedata::get_sum_of_scores($symb,$part,\@BottomSet,
+                                                  undef,$starttime,$endtime);
+    my ($top_sum,$top_max) =
+        &Apache::loncoursedata::get_sum_of_scores($symb,$part,\@TopSet,
+                                                  undef,$starttime,$endtime);
+    my $deg_of_disc;
+    if ($top_max == 0 || $bottom_max==0) {
+        $deg_of_disc = 'nan';
+    } else {
+        $deg_of_disc = ($top_sum/$top_max) - ($bottom_sum/$bottom_max);
+    }
+    #&Apache::lonnet::logthis('    '.$top_sum.'/'.$top_max.
+    #                         ' - '.$bottom_sum.'/'.$bottom_max);
+    return $deg_of_disc;
 }
 
-#---- END Problem Statistics Web Page ----------------------------------------
+###############################################
+###############################################
+##
+## Compute KR-21
+##
+## To compute KR-21, you need the following information:
+##
+## K=the number of items in your test
+## M=the mean score on the test
+## s=the standard deviation of the scores on your test
+##
+## then:
+##
+## KR-21 rk= [K/(K-1)] * [1- (M*(K-M))/(K*s^2))]
+##
+###############################################
+###############################################
+sub compute_sequence_statistics {
+    my ($seq) = @_;
+    my $symb = $seq->symb;
+    my @Resources;
+    my $part_count;
+    foreach my $res (&Apache::lonstathelpers::get_resources($navmap,$seq)) {
+        push (@Resources,$res->symb);
+        $part_count += scalar(@{$res->parts});
+    }
+    my ($starttime,$endtime) = &Apache::lonstathelpers::get_time_limits();
+    #
+    # First compute statistics based on student scores
+    my ($smin,$smax,$sMean,$sSTD,$scount,$sMAX) =
+        &Apache::loncoursedata::score_stats
+                    ([&Apache::lonstatistics::get_selected_sections()],
+                     [&Apache::lonstatistics::get_selected_groups()],
+                     $Apache::lonstatistics::enrollment_status,
+                     \@Resources,$starttime,$endtime,undef);
+    $SeqStat{$symb}->{'title'}  = $seq->compTitle;
+    $SeqStat{$symb}->{'scoremax'}  = $smax;
+    $SeqStat{$symb}->{'scoremin'}  = $smin;
+    $SeqStat{$symb}->{'scoremean'} = $sMean;
+    $SeqStat{$symb}->{'scorestd'}  = $sSTD;
+    $SeqStat{$symb}->{'scorecount'} = $scount;
+    $SeqStat{$symb}->{'max_possible'} = $sMAX;
+    #
+    # Compute statistics based on the number of correct problems
+    # 'correct' is taken to mean
+    my ($cmin,$cmax,$cMean,$cSTD,$ccount)=
+        &Apache::loncoursedata::count_stats
+        ([&Apache::lonstatistics::get_selected_sections()],
+         [&Apache::lonstatistics::get_selected_groups()],
+         $Apache::lonstatistics::enrollment_status,
+         \@Resources,$starttime,$endtime,undef);
+    my $K = $part_count;
+    my $kr_21;
+    if ($K > 1 && $cSTD > 0) {
+        $kr_21 =  ($K/($K-1)) * (1 - $cMean*($K-$cMean)/($K*$cSTD**2));
+    } else {
+        $kr_21 = 'nan';
+    }
+    $SeqStat{$symb}->{'countmax'} = $cmax;
+    $SeqStat{$symb}->{'countmin'} = $cmin;
+    $SeqStat{$symb}->{'countstd'} = $cSTD;
+    $SeqStat{$symb}->{'countmean'} = $cMean;
+    $SeqStat{$symb}->{'count'} = $ccount;
+    $SeqStat{$symb}->{'items'} = $K;
+    $SeqStat{$symb}->{'KR-21'}=$kr_21;
+    return;
+}
+
+
+
+=pod 
+
+=item ProblemStatisticsLegend
+
+=over 4
+
+=item #Stdnts
+Total number of students attempted the problem.
+
+=item Tries
+Total number of tries for solving the problem.
+
+=item Max Tries
+Largest number of tries for solving the problem by a student.
+
+=item Mean
+Average number of tries. [ Tries / #Stdnts ]
+
+=item #YES
+Number of students solved the problem correctly.
+
+=item #yes
+Number of students solved the problem by override.
+
+=item %Wrong
+Percentage of students who tried to solve the problem 
+but is still incorrect. [ 100*((#Stdnts-(#YES+#yes))/#Stdnts) ]
+
+=item DoDiff
+Degree of Difficulty of the problem.  
+[ 1 - ((#YES+#yes) / Tries) ]
+
+=item S.D.
+Standard Deviation of the tries.  
+[ sqrt(sum((Xi - Mean)^2)) / (#Stdnts-1) 
+where Xi denotes every student\'s tries ]
+
+=item Skew.
+Skewness of the students tries.
+[(sqrt( sum((Xi - Mean)^3) / #Stdnts)) / (S.D.^3)]
+
+=item Dis.F.
+Discrimination Factor: A Standard for evaluating the 
+problem according to a Criterion<br>
+
+=item [Criterion to group students into %27 Upper Students - 
+and %27 Lower Students]
+1st Criterion for Sorting the Students: 
+Sum of Partial Credit Awarded / Total Number of Tries
+2nd Criterion for Sorting the Students: 
+Total number of Correct Answers / Total Number of Tries
+
+=item Disc.
+Number of Students had at least one discussion.
+
+=back
+
+=cut
+
+############################################################
+############################################################
 
 1;
 __END__