C:\Old_Data\perlp>perldoc -q "intersection"
Found in C:\Perl64\lib\pods\perlfaq4.pod
  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.


C:\Old_Data\perlp>