Re: Difference between two arrays - is there a better way?

in reply to Difference between two arrays - is there a better way?

Here is my own "clever way", and you can even use it on more than 2 lists.

my %presence;
my $b = 1;
foreach my $ary (\@list1, \@list2, \@list3) {
    foreach(@$ary) {
        $presence{$_} |= $b;
    }
} continue {
    $b *= 2;
}
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Now you can grep in keys %presence. Each value will indicate in what lists the item was found, as a bit mask. Examples:

@list1only = grep { $presence{$_} == 1 } keys %presence;
@list2only = grep { $presence{$_} == 2 } keys %presence;
@list3only = grep { $presence{$_} == 4 } keys %presence;
@lists1and2only = grep { $presence{$_} == 1+2 } keys %presence;
@inall = grep { $presence{$_} == 1+2+4 } keys %presence;
# etc
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