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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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.

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