GD::Graph::Data - Data set encapsulation for GD::Graph


use GD::Graph::Data;


This module encapsulates the data structure that is needed for GD::Graph and friends. An object of this class contains a list of X values, and a number of lists of corresponding Y values. This only really makes sense if the Y values are numerical, but you can basically store anything. Undefined values have a special meaning to GD::Graph, so they are treated with care when stored.

Many of the methods of this module are intended for internal use by GD::Graph and the module itself, and will most likely not be useful to you. Many won't even seem useful to you...


  use GD::Graph::Data;
  use GD::Graph::bars;

  my $data = GD::Graph::Data->new();

  $data->read(file => '/data/sales.dat', delimiter => ',');
  $data = $data->copy(wanted => [2, 4, 5]);

  # Add the newer figures from the database
  use DBI;
  # do DBI things, like connecting to the database, statement
  # preparation and execution

  while (@row = $sth->fetchrow_array)

  my $chart = GD::Graph::bars->new();
  my $gd = $chart->plot($data);

or for quick changes to legacy code

  # Legacy code builds array like this
  @data = ( [qw(Jan Feb Mar)], [1, 2, 3], [5, 4, 3], [6, 3, 7] );

  # And we quickly need to do some manipulations on that
  my $data = GD::Graph::Data->new();

  # And now do all the new stuff that's wanted.
  while (@foo = bar_baz())


$data = GD::Graph::Data->new()

Create a new GD::Graph::Data object.

$data->set_x($np, $value);

Set the X value of point $np to $value. Points are numbered starting with 0. You probably will never need this. Returns undef on failure.


Get the X value of point $np. See "set_x".

$data->set_y($nd, $np, $value);

Set the Y value of point $np in data set $nd to $value. Points are numbered starting with 0, data sets are numbered starting with 1. You probably will never need this. Returns undef on failure.

$data->get_y($nd, $np)

Get the Y value of point $np in data set $nd. See "set_y". This will return undef on an error, but the fact that it returns undef does not mean there was an error (since undefined values can be stored, and therefore returned).

$data->get_y_cumulative($nd, $np)

Get the cumulative value of point $np in data set<$nd>. The cumulative value is obtained by adding all the values of the points $np in the data sets 1 to $nd.


Returns a list of the minimum and maximum x value or the empty list on failure.


Returns a list of the minimum and maximum y value in data set $nd or the empty list on failure.


Returns a list of the minimum and maximum y value in all data sets or the empty list on failure.

$data->add_point($X, $Y1, $Y2 ...)

Adds a point to the data set. The base for the addition is the current number of X values. This means that if you have a data set with the contents

  (X1,  X2)
  (Y11, Y12)
  (Y31, Y32, Y33, Y34)

a $data->add_point(Xx, Y1x, Y2x, Y3x, Y4x) will result in

  (X1,    X2,    Xx )
  (Y11,   Y12,   Y1x)
  (Y21,   undef, Y2x)
  (Y31,   Y32,   Y3x,  Y34)
  (undef, undef, Y4x)

In other words: beware how you use this. As long as you make sure that all data sets are of equal length, this method is safe to use.


Returns the number of data sets.


In list context, returns a list with its first element the number of X values, and the subsequent elements the number of respective Y values for each data set. In scalar context returns the number of points that have an X value set, i.e. the number of data sets that would result from a call to make_strict.


Return a list of all the X values.


Return a list of the Y values for data set $nd. Data sets are numbered from 1. Returns the empty list if $nd is out of range, or if the data set at $nd is empty.

$data->reset() OR GD::Graph::Data->reset()

As an object method: Reset the data container, get rid of all data and error messages. As a class method: get rid of accumulated error messages and possible other crud.


Make all data set lists the same length as the X list by truncating data sets that are too long, and filling data sets that are too short with undef values. always returns a true value.

$data->cumulate(preserve_undef => boolean)

The cumulate parameter will summarise the Y value sets as follows: the first Y value list will be unchanged, the second will contain a sum of the first and second, the third will contain the sum of first, second and third, and so on. Returns undef on failure.

if the argument preserve_undef is set to a true value, then the sum of exclusively undefined values will be preserved as an undefined value. If it is not present or a false value, undef will be treated as zero. Note that this still will leave undefined values in the first data set alone.

Note: Any non-numerical defined Y values will be treated as 0, but you really shouldn't be using this to store that sort of Y data.


Removes all data sets except the ones in the argument list. It will also reorder the data sets in the order given. Returns undef on failure.

To remove all data sets except the first, sixth and second, in that order:

  $data->wanted(1, 6, 2) or die $data->error;


Reverse the order of the data sets.


Copy an 'old' style GD::Graph data structure or another GD::Graph::Data object into this object. This will remove the current data. Returns undef on failure.


Returns a copy of the object, or undef on failure.


Read a data set from a file. This will remove the current data. returns undef on failure. This method uses the standard module Text::ParseWords to parse lines. If you don't have this for some odd reason, don't use this method, or your program will die.

Data file format: The default data file format is tab separated data (which can be changed with the delimiter argument). Comment lines are any lines that start with a #. In the following example I have replaced literal tabs with <tab> for clarity

  # This is a comment, and will be ignored
  # March is missing

Valid arguments are:

file, mandatory. The file name of the file to read from, or a reference to a file handle or glob.

  $data->read(file => '/data/foo.dat') or die $data->error;
  $data->read(file => \*DATA) or die $data->error;
  $data->read(file => $file_handle) or die $data->error;

no_comment, optional. Give this a true value if you don't want lines with an initial # to be skipped.

  $data->read(file => '/data/foo.dat', no_comment => 1);

delimiter, optional. A regular expression that will become the delimiter instead of a single tab.

  $data->read(file => '/data/foo.dat', delimiter => '\s+');
  $data->read(file => '/data/foo.dat', delimiter => qr/\s+/);

$data->error() OR GD::Graph::Data->error()

Returns a list of all the errors that the current object has accumulated. In scalar context, returns the last error. If called as a class method it works at a class level.

This method is inherited, see GD::Graph::Error for more information.

$data->has_error() OR GD::Graph::Data->has_error()

Returns true if the object (or class) has errors pending, false if not. In some cases (see "copy") this is the best way to check for errors.

This method is inherited, see GD::Graph::Error for more information.


As with all Modules for Perl: Please stick to using the interface. If you try to fiddle too much with knowledge of the internals of this module, you could get burned. I may change them at any time. Specifically, I probably won't always keep this implemented as an array reference.


Martien Verbruggen <>

(c) Martien Verbruggen.

All rights reserved. This package is free software; you can redistribute it and/or modify it under the same terms as Perl itself.


GD::Graph, GD::Graph::Error