FAQ 4.43 How do I compute the difference of two arrays? How do I compute the intersection...

Do you have a question? Post it now! No Registration Necessary.  Now with pictures!

This is an excerpt from the latest version perlfaq4.pod, which
comes with the standard Perl distribution. These postings aim to
reduce the number of repeated questions as well as allow the community
to review and update the answers. The latest version of the complete
perlfaq is at http://faq.perl.org .


4.43: How do I compute the difference of two arrays?  How do I compute the
intersection of two arrays?

    Use a hash. Here's code to do both and more. It assumes that each
    element is unique in a given array:

            @union = @intersection = @difference = ();
            %count = ();
            foreach $element (@array1, @array2) { $count++ }
            foreach $element (keys %count) {
                    push @union, $element;
                    push @{ $count > 1 ? \@intersection : \@difference
}, $element;

    Note that this is the *symmetric difference*, that is, all elements in
    either A or in B but not in both. Think of it as an xor operation.


The perlfaq-workers, a group of volunteers, maintain the perlfaq. They
are not necessarily experts in every domain where Perl might show up,
so please include as much information as possible and relevant in any
corrections. The perlfaq-workers also don't have access to every
operating system or platform, so please include relevant details for
corrections to examples that do not work on particular platforms.
Working code is greatly appreciated.

If you'd like to help maintain the perlfaq, see the details in

Site Timeline