Update: this comment was moved from another node where the OP was garbled.

A bit hard to decipher because although you did use code tags you didn't use them properly. Quite a few improvements could be made but a quick solution would be to change your function like so: 

sub strip_US_CA_dup_hols {
    for my $country (@cntry_of_issue) {
        for my $holiday (@{$countries{$country}}) {
            $seen{$holiday}++;
        }
    }
    for my $country (@cntry_of_issue) {
        my $aref = $countries{$country};
        @$aref = grep { $seen{$_} < 2 } @$aref;
    }
}

# Prints:

'US' => [
        '20120116',
        '20120528',
        '20120704',
        '20121122'
      ],
'CA' => [
        '20120521',
        '20120702',
        '20120806',
        '20121008',
        '20121226'
      ]

[download]

In reply to Re: Delete holiday from array of hashes when US & CA share a holiday by tangent
in thread Delete Duplicate CA & US holidays by dirtdog

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