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Posted by PerlFAQ Server on February 25, 2008, 9:03 pm
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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 .
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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.
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