Plot bar chart with GD::Graph

Question

I have data for each and every student, e.g.:

    Student Name         Score
    Jack                  89
    Jill                  70
    Sandy                 40

Now I'm trying to plot these in a bar chart using GD::Graph::Bar, but I see that I can manually declare all the X and Y values from the chart to be plotted.

Since I don't know the names and scores of each of the student (pulled from a text file), I want to be able to do the values automatically,

I was thinking hash keys and values was a good approach. I placed everything in a hash table: %hash(student name)=(score)

Can anyone help me plot this as a bar chart or guide me? Or would you recommend a different approach?

This is the part where I can plot the graph manually by entering the student names:

 my $graph = GD::Graph::bars->new(800, 800);

   @data = ( 
      ["Jack","Jill"],
      ['30','50'],
        );

     $graph->set( 
        x_label           => 'Students',
        y_label           => 'Scores',
        title             => 'Student Vs. Scores',
       y_max_value       => 60,
       y_tick_number     => 8,
       y_label_skip      => 2 
      ) or die $graph->error;

    my $gd = $graph->plot(\@data) or die $graph->error;

    open(IMG, '>file.png') or die $!;
     binmode IMG;
     print IMG $gd->png;

Answer 1

Assuming your data file is as follows, using tab delimiters.

Student Name         Score
Jack                  89
Jill                  70
Sandy                 40

You could do something like this, pushing your x axis and y axis values from your data file to arrays.

use strict;
use warnings;
use CGI qw( :standard );
use GD::Graph::bars;

open my $fh, '<', 'data.txt' or die $!;

my (@x, @y);
while (<$fh>) {
   next if $. == 1;            # skip header line
   push @x, (split /\t/)[0];   # push 'Student Names' into @x array
   push @y, (split /\t/)[1];   # push 'Score' into @y array
}
close $fh;

my $graph = GD::Graph::bars->new(800, 800);

$graph->set( 
             x_label => 'Students',
             y_label => 'Scores',
             title   => 'Student Vs. Scores',
) or warn $graph->error;

my @data = (\@x, \@y);
$graph->plot(\@data) or die $graph->error();

print header(-type=>'image/jpeg'), $graph->gd->jpeg;

Giving you for example:

If you are wanting to use multiple y axis values, assuming you have another tab delimiter column with for example Score2, you could easily do something like this.

my (@x, @y, @y2);
while (<$fh>) {
   next if $. == 1;
   push @x, (split /\t/)[0];
   push @y, (split /\t/)[1];
   push @y2, (split /\t/)[2];
}

And change your @data array to:

my @data = (\@x, \@y, \@y2);

And your result would be: