FAQ 4.65 How can I get the unique keys from two hashes?

Discussion in 'Perl Misc' started by PerlFAQ Server, Feb 26, 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 .

    --------------------------------------------------------------------

    4.65: How can I get the unique keys from two hashes?

    First you extract the keys from the hashes into lists, then solve the
    "removing duplicates" problem described above. For example:

    %seen = ();
    for $element (keys(%foo), keys(%bar)) {
    $seen{$element}++;
    }
    @uniq = keys %seen;

    Or more succinctly:

    @uniq = keys %{{%foo,%bar}};

    Or if you really want to save space:

    %seen = ();
    while (defined ($key = each %foo)) {
    $seen{$key}++;
    }
    while (defined ($key = each %bar)) {
    $seen{$key}++;
    }
    @uniq = keys %seen;



    --------------------------------------------------------------------

    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.
    PerlFAQ Server, Feb 26, 2011
    #1
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