Question

In Chapter 4, Section 4.8 (Computing Union, Intersection, or Difference of Unique Lists), the Perl Cookbook provides this technique for getting the intersection of two lists of integers:

@a = (1, 3, 5, 6, 7, 8);
@b = (2, 3, 5, 7, 9);
...
foreach $e (@a, @b) {
    $union{$e}++ && $isect{$e}++
}
@union = keys %union;
@isect = keys %isect;

I want this to be done (case-insensitively) for two lists of strings. Any efficient method, please?

Answer 1

Array::Utils is what you’re looking for.

use Array::Utils qw(:all);

my @a = qw( a b c d );
my @b = qw( c d e f );

my @isect = intersect(@a, @b);
print join(",",@isect) . "\n";

This produces the expected output of

c,d

Edit: I didn’t notice that you wanted this done case-insensitively. In that case, you can replace @a with map{lc}@a (and likewise with @b).