cookbook

To Find a Recipe, Look in the Cookbook

The Perl Cookbook, by Tom Christiansen and Nat Torkington, shows in Recipes 4.6 and 4.7 how to construct ''seen hashes'' to compare the contents of two lists.

    foreach (@A) { $seenA{$_} = 1 };
    foreach (@B) { $seenB{$_} = 1 };
    foreach (keys %seenA) {
        if ( exists $seenB{$_} ) { 
            push @both, $_;
        } else {
            push @Aonly, $_;
    }
    foreach (keys %seenB) {
        push @Bonly, $_ unless exists $seenA{$_};
    }

But once I had written this code in two different scripts, I wondered whether there already was a module to take care of it?
I searched CPAN but could find no simple implementation of this code. So I wrote my own.