Data::Xtab - Pivot (cross-tabulate) a table of data.

  'A', 'JUN', 7
  'A', 'JAN', 4
  'B', 'JAN', 3
  'B', 'FEB', 39
  'C', 'MAY', 8
  'A', 'JUN', 100

          JAN     FEB     MAR     APR     MAY     JUN
  A       4       0       0       0       0       107
  B       3       39      0       0       0       0
  C       0       0       0       0       8       0

  #!/usr/local/bin/perl

  use Data::Xtab;
  use GIFgraph::lines;
  use CGI;
  $query = new CGI;
  print $query->header("image/gif");

  my @data = ( ['A', 'FEB', 31],
               ['A', 'FEB', 12],
               ['A', 'MAR', 18],
               ['A', 'MAR', 29],
               ['A', 'APR', 142],
               ['B', 'FEB', 217],
               ['B', 'FEB', 14],
               ['B', 'MAR', 121],
               ['B', 'APR', 37],
               ['C', 'MAR', 39],
               ['C', 'MAR', 8],
               ['C', 'APR', 100] );

  # The outputcols parameter is used to enumerate the
  # columns that should be used in the output table, and
  # more importantly, the order in which they should appear.
  #
  my @outputcols = ('JAN', 'FEB', 'MAR', 'APR');

  my $xtab = new Data::Xtab(\@data, \@outputcols);

  my @graph_data = $xtab->graph_data;

  $my_graph = new GIFgraph::lines();

  $my_graph->set( 'x_label' => 'Month',
                  'y_label' => 'Sales',
                  'title' => 'Monthly Sales',
                  'y_max_value' => 450,
                  'y_tick_number' => 5,
                  'y_label_skip' => 2 );
  print $my_graph->plot( \@graph_data );

# -*- Perl -*-
#
# Data::Xtab - cross-tabulate a table of data.
#
# Copyright (c) 1997, Brian C. Jepson
#
# You may distribute this under the same terms as Perl
# itself.
#

$Data::Xtab::VERSION = '1.01';

package Data::Xtab;
use strict;

sub new {

  my $class = shift;

  my $self = {};
  bless($self,$class);

  $self->{data} = shift;
  $self->{cols} = shift;

  $self->pivot;

  return $self;

}

# Pivot the data.
#
sub pivot {

  my $self = shift;

  my %rows;

  # This is the input data.
  #
  my @data = @{ $self->{data} };

  my @cols;
  foreach (@data) {

    # Each row in the input data is a reference to an array
    # of the row_label, column_label, and data value. The 
    # row_label is the value that describes each data series. 
    # The column_label is the value that is used as headers 
    # for each columns, and the data value is the information 
    # that appears cross-referenced between the row_label and
    # column_label values.
    #
    # In the SYNOPSIS section of the documentation, the
    # 'A', 'B' and 'C' values are the row_label values, and 
    # the months (FEB-APR) are the column_label values.
    #
    my $row_label = $$_[0];
    my $column_label = $$_[1];

    # By incrementing the row_label attribute, we ensure
    # that each row_label gets listed in an easy-to-fetch 
    # lookup hash.
    #
    $self->{row_label}->{$row_label}++;

    # By incrementing the column_label attribute, we ensure
    # that each pivoted column gets listed in an 
    # easy-to-fetch lookup hash.
    #
    $self->{column_label}->{$column_label}++;

    # The values are stored in a hash of hashes - keyed
    # first by the row_label, and then by the column_label 
    # value. Note that the values can be cumulative, as you 
    # can have more than one data element that goes into a 
    # given row_label/column_label value "bucket."
    #
    $rows{$row_label}{$column_label} += $$_[2];
  
  }

  # If, for some reason, the user didn't pass in a list of
  # column titles, then we'll sort the keys we have in the
  # column_label attribute, and use that. This is a bad
  # idea, particularly with character month names and data
  # sets that may have gaps. It's best to always explicitly
  # supply the columns.
  #
  @cols = sort keys %{ $self->{column_label} };
  $self->{cols} ||= \@cols;

  return (%{$self->{'rows'}}  = %rows);

}

sub row_labels {
  my ($self) = shift;
  keys %{$self->{row_label}};
}

# massage the cross-tab into something that GIFgraph.pm can
# handle.
#
sub graph_data {
    my $self = shift;

    my %rows = %{$self->{rows}};
    my @graph_data;
    my @header;
    foreach my $col ( @{$self->{cols}}) {
        push @header, $col;
    }
    push @graph_data, \@header;
    my @total;
    foreach my $row ($self->row_labels) {
        my @data;
        my $i;
        foreach my $col (@{$self->{cols}}) {

            my $val = 0;
            if (defined $rows{$row}{$col}) {
                $val = $rows{$row}{$col} * 1;
            }
            push @data, $val;
            $total[$i++] += $val;
        }
        push @graph_data, \@data;
    }
    push @graph_data, \@total;
    @graph_data;
}

1;