--- loncom/interface/statistics/lonproblemstatistics.pm	2004/07/12 19:30:12	1.90
+++ loncom/interface/statistics/lonproblemstatistics.pm	2004/08/04 15:07:42	1.93
@@ -1,6 +1,6 @@
 # The LearningOnline Network with CAPA
 #
-# $Id: lonproblemstatistics.pm,v 1.90 2004/07/12 19:30:12 matthew Exp $
+# $Id: lonproblemstatistics.pm,v 1.93 2004/08/04 15:07:42 matthew Exp $
 #
 # Copyright Michigan State University Board of Trustees
 #
@@ -238,6 +238,17 @@ my @Fields = (
              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  => '#FFDDDD',
+             format => '%4.1f',
+             sortable  => 'yes',
+             graphable => 'yes',
              long_title => 'Percent of students whose final answer is wrong',
              selectable => 'yes',
              defaultselected => 'yes',
@@ -819,7 +830,7 @@ sub statistics_html_table_data {
         if (exists($field->{'special'}) && $field->{'special'} eq 'link') {
             $row .= '<a href="'.$data->{$field->{'name'}.'.link'}.'">';
         }
-        if (exists($field->{'format'})) {
+        if (exists($field->{'format'}) && $data->{$field->{'name'}} !~ /[A-Z]/i) {
             $row .= sprintf($field->{'format'},$data->{$field->{'name'}});
         } else {
             $row .= $data->{$field->{'name'}};
@@ -1581,6 +1592,10 @@ sub compute_discrimination_factor {
         map { 
             $_->[&Apache::loncoursedata::RNK_student()]; 
           } @{$ranking}[($num_students-$number_to_grab)..($num_students-1)];
+    if (! @BottomSet || (@BottomSet == 1 && $BottomSet[0] eq '') ||
+        ! @TopSet    || (@TopSet    == 1 && $TopSet[0]    eq '')) {
+        return 'nan';
+    }
     my ($bottom_sum,$bottom_max) = 
         &Apache::loncoursedata::get_sum_of_scores($resource,$part,\@BottomSet,
                                                   undef,$starttime,$endtime);