Or more generally: a way to invert a hash (keys become values and vice versa) without loosing any data:
use strict;
use warnings;
use Data::Dumper;

my %hash;
while (<DATA>) {
    my ( $key, $value ) = split;
    $hash{$key} = $value;
} ## end while (<DATA>)
print "Original hash\n", Dumper( \%hash );

my %data_structure;
foreach my $key ( keys %hash ) {
    push @{ $data_structure{ $hash{$key} } }, $key;
} ## end foreach my $key ( keys %hash)
print "Inverted hash\n", Dumper( \%data_structure );

__DATA__
key1, value1
key2, value2
key3, value1
key4, value3
key5, value2
key6, value4
key7, value4

[download]
output
Original hash
$VAR1 = {
          'key3,' => 'value1',
          'key2,' => 'value2',
          'key4,' => 'value3',
          'key6,' => 'value4',
          'key7,' => 'value4',
          'key5,' => 'value2',
          'key1,' => 'value1'
        };
Inverted hash
$VAR1 = {
          'value4' => [
                        'key6,',
                        'key7,'
                      ],
          'value1' => [
                        'key3,',
                        'key1,'
                      ],
          'value3' => [
                        'key4,'
                      ],
          'value2' => [
                        'key2,',
                        'key5,'
                      ]
        };

[download]
The resulting data-structure is a Hash-of-Arrays.

CountZero

A program should be light and agile, its subroutines connected like a string of pearls. The spirit and intent of the program should be retained throughout. There should be neither too little or too much, neither needless loops nor useless variables, neither lack of structure nor overwhelming rigidity." - The Tao of Programming, 4.1 - Geoffrey James

In reply to Re: Creating Array from Hash that pulls only Unique values while iterating over each Unique Value by CountZero
in thread Creating Array from Hash that pulls only Unique values while iterating over each Unique Value by kdmurphy001

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