GD::Graph with Perl - perl

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 since I'm pretty new to perl and modules, I see that I can manually declare all the X and Y values from the chart to be plotted.
But 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. So 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?
Thanks
"Update
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:

Answer 2

According to the documentation, you need to pass an array of arrays to the plot method of GD::Graph::bars. It sounds like you already have a hash so you need to convert it to an array of arrays. There are a number of ways to do this, but here's an example:
#!/usr/bin/perl
use strict;
use warnings;
use Data::Dumper;
my %hash = (
Larry => 15,
Curly => 16,
Moe => 20
);
my (#names, #scores);
while (my ($name, $score) = each %hash) {
push #names, $name;
push #scores, $score;
}
my #data = (\#names, \#scores);
print Dumper(\#data);
# $VAR1 = [
# [
# 'Moe',
# 'Curly',
# 'Larry'
# ],
# [
# 20,
# 16,
# 15
# ]
# ];
However you do it, make sure you preserve the order in the inner arrays.

Answer 3

I adapted the code from the samples directory in GD::Graph:
use warnings;
use strict;
use GD::Graph::bars;
use GD::Graph::Data;
my %students = (
Jack => 89,
Jill => 70,
Sandy => 40,
);
my #scores;
my #names;
for (keys %students) {
push #names, $_;
push #scores, $students{$_};
}
my $data = GD::Graph::Data->new([
[#names],
[#scores],
]) or die GD::Graph::Data->error;
my $my_graph = GD::Graph::bars->new();
$my_graph->set(
x_label => 'Name',
y_label => 'Score',
title => 'A Simple Bar Chart',
) or warn $my_graph->error;
$my_graph->plot($data) or die $my_graph->error();
save_chart($my_graph, 'graph');
sub save_chart {
my $chart = shift or die "Need a chart!";
my $name = shift or die "Need a name!";
local(*OUT);
my $ext = $chart->export_format;
open(OUT, ">$name.$ext") or
die "Cannot open $name.$ext for write: $!";
binmode OUT;
print OUT $chart->gd->$ext();
close OUT;
}