Untested: 
my %holiday;
while (<DATA>) {
   my (undef, undef, $cc, undef, undef, $date) = split /,/;
   $holiday{$cc}{$date} = 1;
}
delete $holiday{US}{$_} for keys %{$holiday{CA}};
delete $holiday{CA}{$_} for keys %{$holiday{US}};
# Turn into a hash of array:
$holiday{$_} = [sort keys %{$holiday{$_}}] for qw[US CA];

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In reply to Re: Delete Duplicate CA & US holidays by JavaFan
in thread Delete Duplicate CA & US holidays by dirtdog

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