Hashes are a good way to have what you want. The data you show can be easily collected into a multi-layer hash, with ProductionLine as the top-level key, DayOfWeek as the second-level key, and Output as the value. (You can flip the top- and second-layer keys if it is more convenient to think of the data that way; I like the ProductionLine at the top, especially if you are going to end up plotting based on Line).

The code snippet below should get you started.

You should also have a look at perldsc and perlreftut for some basic training in complex data structures in Perl.

use strict;
use warnings;
use Data::Dumper;

my %outputs;

while ( <DATA> ) {
    my($day, $line, $output) = (split);
    $outputs{$line}{$day} = $output;
}

print Dumper(\%outputs);

__END__
2    CANNING     18353
2    MULTIPACK    14878
2    QUEST    911
3    CANNING    46775
3    MULTIPACK    42601
3    QUEST    1564
4    CANNING    81302
4    MULTIPACK    67542
4    QUEST    1879
[download]

---

Output:

$VAR1 = {
          'CANNING' => {
                         '4' => '81302',
                         '3' => '46775',
                         '2' => '18353'
                       },
          'QUEST' => {
                       '4' => '1879',
                       '3' => '1564',
                       '2' => '911'
                     },
          'MULTIPACK' => {
                           '4' => '67542',
                           '3' => '42601',
                           '2' => '14878'
                         }
        };
[download]