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

Discussion in 'Perl Misc' started by PerlFAQ Server, Feb 2, 2011.

  1. 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
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    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.

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    perlfaq.pod.
    PerlFAQ Server, Feb 2, 2011
    #1
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