File:  [LON-CAPA] / loncom / interface / statistics / lonproblemstatistics.pm
Revision 1.83: download - view: text, annotated - select for diffs
Tue Apr 6 15:45:13 2004 UTC (20 years, 2 months ago) by matthew
Branches: MAIN
CVS tags: HEAD
Moved storage of dynamic metadata from loncoursedata to lonproblemstatistics.
lonproblemstatistics now only stores the dynamic metadata when the stats are
computed for all sections.
Discrimination factor computations now respect start and end times.
Modified loncoursedata::rank_students_by_scores_on_resources and
loncoursedata::get_sum_of_scores to support time constraints.

# The LearningOnline Network with CAPA
#
# $Id: lonproblemstatistics.pm,v 1.83 2004/04/06 15:45:13 matthew Exp $
#
# Copyright Michigan State University Board of Trustees
#
# This file is part of the LearningOnline Network with CAPA (LON-CAPA).
#
# LON-CAPA is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# LON-CAPA is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with LON-CAPA; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
#
# /home/httpd/html/adm/gpl.txt
#
# http://www.lon-capa.org/
#
# (Navigate problems for statistical reports
#
###############################################
###############################################

=pod

=head1 NAME

lonproblemstatistics

=head1 SYNOPSIS

Routines to present problem statistics to instructors via tables,
Excel files, and plots.

=over 4

=cut

###############################################
###############################################

package Apache::lonproblemstatistics;

use strict;
use Apache::lonnet();
use Apache::loncommon();
use Apache::lonhtmlcommon;
use Apache::loncoursedata;
use Apache::lonstatistics;
use Apache::lonlocal;
use Spreadsheet::WriteExcel;
use Apache::lonstathelpers();
use Time::HiRes;

my @StatsArray;
my %SeqStat;    # keys are symbs, values are hash refs

##
## Localization notes:
##
## in @Fields[0]->{'long_title'} is placed in Excel files and is used as the
## header for plots created with Graph.pm, both of which more than likely do
## not support localization.
##
#
#
##
## 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.  NOT translated
## 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?
##
my @Fields = (
           { name => 'problem_num',
             title => 'P#',
             align => 'right',
             color => '#FFFFE6',
             selectable => 'no',
             defaultselected => 'yes',
           },
           { name   => 'container',
             title  => 'Sequence or Folder',
             align  => 'left',
             color  => '#FFFFE6',
             sortable => 'yes',
             selectable => 'no',
             defaultselected => 'yes',
           },
           { name   => 'title',
             title  => 'Title',
             align  => 'left',
             color  => '#FFFFE6',
             special  => 'link',
             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',
             color  => '#EEFFCC',
             format => '%d',
             sortable  => 'yes',
             graphable => 'yes',
             long_title => 'Number of Students Attempting Problem',
             selectable => 'yes',
             defaultselected => 'yes',
           },
           { name   => 'tries',
             title  => 'Tries',
             align  => 'right',
             color  => '#EEFFCC',
             format => '%d',
             sortable  => 'yes',
             graphable => 'yes',
             long_title => 'Total Number of Tries',
             selectable => 'yes',
             defaultselected => 'yes',
           },
           { name   => 'max_tries',
             title  => 'Max Tries',
             align  => 'right',
             color  => '#DDFFFF',
             format => '%d',
             sortable  => 'yes',
             graphable => 'yes',
             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',
             color  => '#DDFFFF',
             format => '%5.2f',
             sortable  => 'yes',
             graphable => 'yes',
             long_title => 'Average Number of Tries',
             selectable => 'yes',
             defaultselected => 'yes',
           },
           { name   => 'std_tries',
             title  => 'S.D. tries',
             align  => 'right',
             color  => '#DDFFFF',
             format => '%5.2f',
             sortable  => 'yes',
             graphable => 'yes',
             long_title => 'Standard Deviation of Number of Tries',
             selectable => 'yes',
             defaultselected => 'yes',
           },
           { name   => 'skew_tries',
             title  => 'Skew Tries',
             align  => 'right',
             color  => '#DDFFFF',
             format => '%5.2f',
             sortable  => 'yes',
             graphable => 'yes',
             long_title => 'Skew of Number of Tries',
             selectable => 'yes',
             defaultselected => 'no',
           },
           { name   => 'num_solved',
             title  => '#YES',
             align  => 'right',
             color  => '#FFDDDD',
             format => '%4.1f',#             format => '%d',
             sortable  => 'yes',
             graphable => 'yes',
             long_title => 'Number of Students able to Solve',
             selectable => 'yes',
             defaultselected => 'yes',
           },
           { name   => 'num_override',
             title  => '#yes',
             align  => 'right',
             color  => '#FFDDDD',
             format => '%4.1f',#             format => '%d',
             sortable  => 'yes',
             graphable => 'yes',
             long_title => 'Number of Students given Override',
             selectable => 'yes',
             defaultselected => 'yes',
           },
           { name   => 'num_wrong',
             title  => '#Wrng',
             align  => 'right',
             color  => '#FFDDDD',
             format => '%4.1f',
             sortable  => 'yes',
             graphable => 'yes',
             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 => 'no',
           },
);

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 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";
}

###############################################
###############################################

=pod 

=item &CreateInterface()

Create the main intereface for the statistics page.  Allows the user to
select sections, maps, and output.

=cut

###############################################
###############################################
sub CreateInterface {
    #
    &parse_field_selection();
    #
    my $Str = '';
    $Str .= &Apache::lonhtmlcommon::breadcrumbs
        (undef,'Overall Problem Statistics','Statistics_Overall_Key');
    $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('Statistics').'</b></td>';
    $Str .= '<td rowspan="2">'.
        &Apache::lonstathelpers::limit_by_time_form().'</td>';
    $Str .= '</tr>'."\n";
    #
    $Str .= '<tr><td align="center">'."\n";
    $Str .= &Apache::lonstatistics::SectionSelect('Section','multiple',5);
    $Str .= '</td><td align="center">';
    $Str .= &Apache::lonhtmlcommon::StatusOptions(undef,undef,5);
    $Str .= '</td><td align="center">';
    #
    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>'.&field_selection_input();
    $Str .= '</td></tr>'."\n";
    $Str .= '</table>'."\n";
    $Str .= '<input type="submit" name="GenerateStatistics" value="'.
        &mt('Generate Statistics').'" />';
    $Str .= '&nbsp;'x5;
    $Str .= 'Plot '.&plot_dropdown().('&nbsp;'x10);
    $Str .= '<input type="submit" name="ClearCache" value="'.
        &mt('Clear Caches').'" />';
    $Str .= '&nbsp;'x5;
    $Str .= '<input type="submit" name="UpdateCache" value="'.
        &mt('Update Student Data').'" />';
    $Str .= '&nbsp;'x5;
    $Str .= '<input type="submit" name="Excel" value="'.
        &mt('Produce Excel Output').'" />';
    $Str .= '&nbsp;'x5;
    return $Str;
}

###############################################
###############################################

=pod 

=item &BuildProblemStatisticsPage()

Main interface to problem statistics.

=cut

###############################################
###############################################
sub BuildProblemStatisticsPage {
    my ($r,$c)=@_;
    #
    my %Saveable_Parameters = ('Status' => 'scalar',
                               'statsoutputmode' => 'scalar',
                               'Section' => 'array',
                               'StudentData' => 'array',
                               'Maps' => 'array',
                               'fieldselections'=> 'array');
    &Apache::loncommon::store_course_settings('statistics',
                                              \%Saveable_Parameters);
    &Apache::loncommon::restore_course_settings('statistics',
                                                \%Saveable_Parameters);
    #
    &Apache::lonstatistics::PrepareClasslist();
    #
    # Clear the package variables
    undef(@StatsArray);
    undef(%SeqStat);
    #
    # Finally let the user know we are here
    my $interface = &CreateInterface();
    $r->print($interface);
    $r->print('<input type="hidden" name="sortby" value="'.$ENV{'form.sortby'}.
              '" />');
    #
    if (! exists($ENV{'form.statsfirstcall'})) {
        $r->print('<input type="hidden" name="statsfirstcall" value="yes" />');
        $r->print('<h3>'.
                  &mt('Press "Generate Statistics" when you are ready.').
                  '</h3><p>'.
                  &mt('It may take some time to update the student data '.
                      'for the first analysis.  Future analysis this session '.
                      ' will not have this delay.').
                  '</p>');
        return;
    } elsif ($ENV{'form.statsfirstcall'} eq 'yes' || 
             exists($ENV{'form.UpdateCache'}) ||
             exists($ENV{'form.ClearCache'}) ) {
        $r->print('<input type="hidden" name="statsfirstcall" value="no" />');
        &Apache::lonstatistics::Gather_Student_Data($r);
    } else {
        $r->print('<input type="hidden" name="statsfirstcall" value="no" />');
    }
    $r->rflush();
    #
    # This probably does not need to be done each time we are called, but
    # it does not slow things down noticably.
    &Apache::loncoursedata::populate_weight_table();
    #
    if (exists($ENV{'form.Excel'})) {
        &Excel_output($r);
    } else {
        my $count = 0;
        foreach my $seq (&Apache::lonstatistics::Sequences_with_Assess()) {
            $count += $seq->{'num_assess_parts'};
        }
        if ($count > 10) {
            $r->print('<h2>'.
                      &mt('Compiling statistics for [_1] problems',$count).
                      '</h2>');
            if ($count > 30) {
                $r->print('<h3>'.&mt('This will take some time.').'</h3>');
            }
            $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);
        }
    }
    return;
}

sub output_sequence_statistics {
    my ($r) = @_;
    my $c=$r->connection();
    $r->print('<h2>'.&mt('Sequence Statistics').'</h2>');
    $r->print('<table border="0"><tr><td bgcolor="#777777">'."\n".
              '<table border="0" cellpadding="3">'."\n".
              '<tr bgcolor="#FFFFE6">');
    $r->print(&sequence_html_header());
    foreach my $seq (&Apache::lonstatistics::Sequences_with_Assess()) {
        last if ($c->aborted);
        next if ($seq->{'num_assess'} < 1);
        &compute_sequence_statistics($seq);
        $r->print(&sequence_html_output($seq));
    }
    $r->print('</table>');
    $r->print('</table>');
    $r->rflush();
    return;
}


##########################################################
##########################################################
##
## HTML output routines
##
##########################################################
##########################################################
sub output_html_by_sequence {
    my ($r) = @_;
    my $c = $r->connection();
    $r->print(&html_preamble());
    #
    foreach my $seq (&Apache::lonstatistics::Sequences_with_Assess()) {
        last if ($c->aborted);
        next if ($seq->{'num_assess'} < 1);
        $r->print("<h3>".$seq->{'title'}."</h3>".
                  '<table border="0"><tr><td bgcolor="#777777">'."\n".
                  '<table border="0" cellpadding="3">'."\n".
                  '<tr bgcolor="#FFFFE6">'.
                  &statistics_table_header('no container')."</tr>\n");
        my @Data = &compute_statistics_on_sequence($seq);
        foreach my $data (@Data) {
            $r->print('<tr>'.&statistics_html_table_data($data,
                                                         'no container').
                      "</tr>\n");
        }
        $r->print('</table>'."\n".'</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("</table>\n</table>\n");
            $r->print('<table border="0"><tr><td bgcolor="#777777">'."\n".
                      '<table border="0" cellpadding="3">'."\n".
                      '<tr bgcolor="#FFFFE6">'.
                      '<tr bgcolor="#FFFFE6">'.
                      &statistics_table_header().
                      "</tr>\n");
        }
        $r->print('<tr>'.&statistics_html_table_data($data)."</tr>\n");
    }
    $r->print("</table>\n</table>\n");
    return;
}

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 .= "<h3>".&mt('Compiled on [_1]',
                       &Apache::lonlocal::locallocaltime(time))."</h3>";
    return $Str;
}


###############################################
###############################################
##
## 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');
        $row .= '<td bgcolor="'.$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'}});
        } else {
            $row .= $data->{$field->{'name'}};
        }
        if (exists($field->{'special'}) && $field->{'special'} eq 'link') {
            $row.= '</a>';
        }
        $row .= '</td>';
    }
    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;
}

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;
}


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;
}

####################################################
####################################################
##
##    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 make_single_stat_plot {
    my ($r,$datafield) = @_;
    #
    my $title; my $yaxis;
    foreach my $field (@Fields) {
        next if ($field->{'name'} ne $datafield);
        $title = $field->{'long_title'};
        $yaxis = $field->{'title'};
        last;
    }
    if ($title eq '' || $yaxis eq '') {
        # datafield is something we do not know enough about to plot
        $r->print('<h3>'.
                  &mt('Unable to plot the requested statistic.').
                  '</h3>');
        return;
    }
    #
    # 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 = $_;
            last;
        }
    }
    if ($max > 20000) {
        $max = 10000*(int($max/10000)+1);
    }
    #
    $r->print("<p>".&Apache::loncommon::DrawBarGraph($title,
                                                     '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;
        }
    }
    #
    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);
        }
    }
    #
    my $discdata .= '<data>'.join(',',@Labels).'</data>'.$/.
                    '<data>'.join(',',@Disc).'</data>'.$/;
    #
    my $diffdata .= '<data>'.join(',',@Labels).'</data>'.$/.
                    '<data>'.join(',',@Diff).'</data>'.$/;
    #
    my $title = 'Degree of Discrimination\nand Degree of Difficulty';
    if ($xmax > 50) {
        $title = 'Degree of Discrimination and Degree of Difficulty';
    }
    #
    $plot=<<"END";
<gnuplot 
    texfont="10"
    fgcolor="x000000"
    plottype="Cartesian"
    font="large"
    grid="on"
    align="center"
    border="on"
    transparent="on"
    alttag="Degree of Discrimination and Degree of Difficulty Plot"
    samples="100"
    bgcolor="xffffff"
    height="$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>Problem Number</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);
        }
    }
    $ymax = int($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 $title = 'Mean and S.D. of Tries';
    if ($xmax > 25) {
        $title = 'Mean and Standard Deviation of Tries';
    }
    #
    $plot=<<"END";
<gnuplot 
    texfont="10"
    fgcolor="x000000"
    plottype="Cartesian"
    font="large"
    grid="on"
    align="center"
    border="on"
    transparent="on"
    alttag="Mean and S.D of Tries Plot"
    samples="100"
    bgcolor="xffffff"
    height="$height"
    width="$width">
    <title>$title</title>
    <axis xmin="0" ymin="0" xmax="$xmax" ymax="$ymax" color="x000000" />
    <xlabel>Problem Number</xlabel>
    <ylabel>Number of Tries</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 $current = '';
    #
    if (defined($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">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 ';
        }
        $Str.= '>'.&mt($field->{'title'}).'</option>'."\n";
    }
    $Str .= '</select>'."\n";
    return $Str;
}

###############################################
###############################################
##
## Excel output routines
##
###############################################
###############################################
sub Excel_output {
    my ($r) = @_;
    $r->print('<h2>'.&mt('Preparing Excel Spreadsheet').'</h2>');
    ##
    ## Compute the statistics
    &compute_all_statistics($r);
    my $c = $r->connection;
    return if ($c->aborted());
    ##
    ## Create the excel workbook
    my $filename = '/prtspool/'.
        $ENV{'user.name'}.'_'.$ENV{'user.domain'}.'_'.
        time.'_'.rand(1000000000).'.xls';
    my ($starttime,$endtime) = &Apache::lonstathelpers::get_time_limits();
    #
    # Create sheet
    my $excel_workbook = Spreadsheet::WriteExcel->new('/home/httpd'.$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 0;
    }
    #
    # 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);
    #
    # Add a worksheet
    my $sheetname = $ENV{'course.'.$ENV{'request.course.id'}.'.description'};
    if (length($sheetname) > 31) {
        $sheetname = substr($sheetname,0,31);
    }
    my $excel_sheet = $excel_workbook->addworksheet(
        &Apache::loncommon::clean_excel_name($sheetname));
    #
    my $format = &Apache::loncommon::define_excel_formats($excel_workbook);
    ##
    ## 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'},
                        $format->{'h1'});
    $cols_output += 3;
    #
    # Put a description of the sections listed
    my $sectionstring = '';
    $excel_sheet->write($rows_output,$cols_output++,
                        &Apache::lonstathelpers::sections_description
                            (@Apache::lonstatistics::SelectedSections),
                        $format->{'h3'});
    $cols_output += scalar(@Apache::lonstatistics::SelectedSections);
    #
    # 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;
    }
    #
    # Put the date in there too
    $excel_sheet->write($rows_output,$cols_output++,
                        'Compiled on '.localtime(time));
    #
    $rows_output++; 
    $cols_output=0;
    ##
    ## Sequence Statistics
    ## 
    &write_headers($excel_sheet,$format,\$rows_output,\$cols_output,
                   \@SeqFields);
    foreach my $seq (&Apache::lonstatistics::Sequences_with_Assess()) {
        next if ($seq->{'num_assess'} < 1);
        my $data = $SeqStat{$seq->{'symb'}};
        $cols_output=0;
        foreach my $field (@SeqFields) {
            next if ($field->{'selected'} ne 'yes');
            $excel_sheet->write($rows_output,$cols_output++,
                                $data->{$field->{'name'}});
        }
        $rows_output++;
        $cols_output=0;
    }
    ##
    ## Resource Statistics
    ##
    $rows_output++;
    $cols_output=0;
    &write_headers($excel_sheet,$format,\$rows_output,\$cols_output,
                   \@Fields);
    #
    foreach my $data (@StatsArray) {
        $cols_output=0;
        foreach my $field (@Fields) {
            next if ($field->{'selected'} ne 'yes');
            next if ($field->{'name'} eq 'problem_num');
            $excel_sheet->write($rows_output,$cols_output++,
                                $data->{$field->{'name'}});
        }
        $rows_output++;
        $cols_output=0;
    }
    #
    $excel_workbook->close();
    #
    # Tell the user where to get their excel file
    $r->print('<br />'.
              '<a href="'.$filename.'">'.
              &mt('Your Excel Spreadsheet').'</a>'."\n");
    $r->rflush();
    return;
}

##
## &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($$rows_output,${$cols_output},
                                $field->{'long_title'},
                                $format->{'bold'});
        } else {
            $excel_sheet->write($$rows_output,${$cols_output},'');
        }
        ${$cols_output}+= 1;
    }
    ${$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;
}

##################################################
##################################################
##
## Statistics Gathering and Manipulation Routines
##
##################################################
##################################################
sub compute_statistics_on_sequence {
    my ($seq) = @_;
    my @Data;
    foreach my $res (@{$seq->{'contents'}}) {
        next if ($res->{'type'} ne 'assessment');
        foreach my $part (@{$res->{'parts'}}) {
            #
            # This is where all the work happens
            my $data = &get_statistics($seq,$res,$part,scalar(@StatsArray)+1);
            push (@Data,$data);
            push (@StatsArray,$data);
        }
    }
    return @Data;
}

sub compute_all_statistics {
    my ($r) = @_;
    if (@StatsArray > 0) {
        # Assume we have already computed the statistics
        return;
    }
    my $c = $r->connection;
    foreach my $seq (&Apache::lonstatistics::Sequences_with_Assess()) {
        last if ($c->aborted);
        next if ($seq->{'num_assess'} < 1);
        &compute_sequence_statistics($seq);
        &compute_statistics_on_sequence($seq);
    }
}

sub sort_data {
    my ($sortkey) = @_;
    return if (! @StatsArray);
    #
    # Sort the data
    my $sortby = undef;
    foreach my $field (@Fields) {
        if ($sortkey eq $field->{'name'}) {
            $sortby = $field->{'name'};
        }
    }
    if (! defined($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 {
            # 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;
        }
    }
    #
    # 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 ($starttime,$endtime) = &Apache::lonstathelpers::get_time_limits();
    my $symb = $resource->{'symb'};
    my $courseid = $ENV{'request.course.id'};
    #
    my $data = &Apache::loncoursedata::get_problem_statistics
                        (\@Apache::lonstatistics::SelectedSections,
                         $Apache::lonstatistics::enrollment_status,
                         $symb,$part,$courseid,$starttime,$endtime);
    $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'});
    #
    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 ($Apache::lonstatistics::SelectedSections[0] eq 'all' &&
        $data->{'num_students'} > 1) {
        my %storestats;
        #
        my $urlres=(&Apache::lonnet::decode_symb($resource->{'symb'}))[2];
        my ($dom,$user) = $urlres=~/^(\w+)\/(\w+)/; 
        my $preamble = $courseid.'___'.$urlres.'___';
        #
        $storestats{$preamble.'timestamp'}  = time;
        $storestats{$preamble.'stdno'}      = $data->{'num_students'};
        $storestats{$preamble.'avetries'}   = $data->{'mean_tries'};
        $storestats{$preamble.'difficulty'} = $data->{'deg_of_diff'};
        if ($SelectedFields{'deg_of_disc'}) {
            $storestats{$preamble.'discrimination'} = $data->{'deg_of_disc'};
        }
        #
        &Apache::lonnet::put('nohist_resevaldata',\%storestats,$dom,$user);
    }
    return $data;
}

###############################################
###############################################

=pod

=item &compute_discrimination_factor()

Inputs: $Resource, $Sequence

Returns: integer between -1 and 1

=cut

###############################################
###############################################
sub compute_discrimination_factor {
    my ($resource,$part,$sequence) = @_;
    my @Resources;
    foreach my $res (@{$sequence->{'contents'}}) {
        next if ($res->{'symb'} eq $resource->{'symb'});
        push (@Resources,$res->{'symb'});
    }
    #
    # rank
    my ($starttime,$endtime) = &Apache::lonstathelpers::get_time_limits();
    my $ranking = 
        &Apache::loncoursedata::rank_students_by_scores_on_resources
        (\@Resources,
         \@Apache::lonstatistics::SelectedSections,
         $Apache::lonstatistics::enrollment_status,undef,
         $starttime,$endtime);
    #
    # 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}[($num_students-$number_to_grab)..($num_students-1)];
    my ($bottom_sum,$bottom_max) = 
        &Apache::loncoursedata::get_sum_of_scores($resource,$part,\@BottomSet,
                                                  undef,$starttime,$endtime);
    my ($top_sum,$top_max) = 
        &Apache::loncoursedata::get_sum_of_scores($resource,$part,\@TopSet,
                                                  undef,$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;
}

###############################################
###############################################
##
## 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;
    foreach my $res (@{$seq->{'contents'}}) {
        next if ($res->{'type'} ne 'assessment');
        push (@Resources,$res->{'symb'});
    }
    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::SelectedSections,
                     $Apache::lonstatistics::enrollment_status,
                     \@Resources,$starttime,$endtime,undef);
    $SeqStat{$symb}->{'title'}  = $seq->{'title'};
    $SeqStat{$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::SelectedSections,
         $Apache::lonstatistics::enrollment_status,
         \@Resources,$starttime,$endtime,undef);
    my $K = $seq->{'num_assess_parts'};
    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__

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