FAQ 4.43 How do I compute the difference of two arrays? How do I compute the intersection of two arrays?
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From: PerlFAQ Server on 31 May 2010 12:00 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) { $count{$element}++ } foreach $element (keys %count) { push @union, $element; push @{ $count{$element} > 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 perlfaq.pod. |