If the sets contain integers in a reasonable range you could use indexing, like this:

use strict;
use PDL;
 
my $pdl_a = pdl 10..20;
my $pdl_b = pdl 15..18;
my $mask_a = zeroes 21;
my $mask_b = zeroes 21;
my $set_a = index($mask_a, $pdl_a);
my $set_b = index($mask_b, $pdl_b);
$set_a .= 1;
$set_b .= 1;
my $pdl_c = which($mask_a & $mask_b);
print $pdl_c,"\n";
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If the sets are large you could use bit masking, as in this example: Re^2: Basic Perl trumps DBI? Or my poor DB design?.