The following requires an additional hash and an additional array, but both contain only pointers, so overhead should be extremely low. Enjoy... 
$var = [
{
'id_a' => '1',
'id_b' => '5',
'value_x' => '10',
'value_y' => '5'
},
{
'id_a' => '2',
'id_b' => '3',
'value_x' => '20',
'value_y' => '10'
},
{
'id_a' => '2',
'id_b' => '3',
'value_x' => '30',
'value_y' => '20'
},
{
'id_a' => '3',
'id_b' => '7',
'value_x' => '15',
'value_y' => '15'
}];

my ($id, %ids, @var2);
for (my $i = 0; $i <= $#$var; $i++) {
    $id = @$var[$i]->{'id_a'} . ' ' . @$var[$i]->{'id_b'};
    if (!$ids{$id}) {
        push(@var2, @$var[$i]);
        $ids{$id} = @$var[$i];
    }
    else {
        $ids{$id}->{'value_x'} += @$var[$i]->{'value_x'};
        $ids{$id}->{'value_y'} += @$var[$i]->{'value_y'};
    }
}
$var = \@var2;

foreach (@$var) {
    print '[' . $line++ . ']' .
          ' id_a -> ' . $_->{'id_a'} .
          ' id_b -> ' . $_->{'id_b'} .
          ' value_x -> ' . $_->{'value_x'} .
          ' value_y -> ' . $_->{'value_y'} . "\n";
}

[download]
You can cut the last part if you want - that's only to demonstrate that the code works.

In reply to Re: Messing about in Arrays of Hashes by TedPride
in thread Messing about in Arrays of Hashes by nzgrover

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