--- loncom/interface/statistics/lonproblemstatistics.pm	2004/03/07 21:42:19	1.70
+++ loncom/interface/statistics/lonproblemstatistics.pm	2004/03/23 16:35:15	1.71
@@ -1,6 +1,6 @@
 # The LearningOnline Network with CAPA
 #
-# $Id: lonproblemstatistics.pm,v 1.70 2004/03/07 21:42:19 matthew Exp $
+# $Id: lonproblemstatistics.pm,v 1.71 2004/03/23 16:35:15 matthew Exp $
 #
 # Copyright Michigan State University Board of Trustees
 #
@@ -58,7 +58,7 @@ use Apache::lonstatistics;
 use Apache::lonlocal;
 use Spreadsheet::WriteExcel;
 use Apache::lonstathelpers();
-
+use Time::HiRes;
 ##
 ## Localization notes:
 ##
@@ -168,6 +168,15 @@ my @Fields = (
              sortable  => 'yes',
              graphable => 'yes',
              long_title => 'Percent of students whose final answer is wrong' },
+           { name   => 'deg_of_disc',
+             title  => 'Deg of Disc',
+             align  => 'right',
+             color  => '#FFFFE6',
+             format => '%4.2f',
+             sortable  => 'yes',
+             graphable => 'yes',
+             long_title => 'Degree of Discrimination' },
+
 );
 
 ###############################################
@@ -283,6 +292,8 @@ sub BuildProblemStatisticsPage {
     #
     &Apache::lonstatistics::PrepareClasslist();
     #
+    &Apache::loncoursedata::populate_weight_table();
+    #
     my ($interface,$output_mode,$show) = &CreateInterface();
     $r->print($interface);
     $r->print('<input type="hidden" name="statsfirstcall" value="no" />');
@@ -849,9 +860,66 @@ sub get_statistics {
     $data->{'title.link'}  = $resource->{'src'}.'?symb='.
         &Apache::lonnet::escape($resource->{'symb'});
     #
+    $data->{'deg_of_disc'} = &compute_discrimination_factor($resource,$part,$sequence);
     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) = @_;
+    &Apache::lonnet::logthis($sequence->{'title'}.' '.$resource->{'title'});
+    my @Resources;
+    foreach my $res (@{$sequence->{'contents'}}) {
+        next if ($res->{'symb'} eq $resource->{'symb'});
+        push (@Resources,$res->{'symb'});
+    }
+    #
+    # rank
+    my $ranking = 
+        &Apache::loncoursedata::rank_students_by_scores_on_resources
+        (\@Resources,
+         \@Apache::lonstatistics::SelectedSections,
+         $Apache::lonstatistics::enrollment_status,undef);
+    #
+    # 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,$part,\@BottomSet);
+    my ($top_sum,$top_max) = 
+        &Apache::loncoursedata::get_sum_of_scores($resource,$part,\@TopSet);
+    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;
+}
+
 ###############################################
 ###############################################