In Perl, how can I generate all possible combinations of a list?

Question

I have a file with a list, and a need to make a file that compares each line to the other. for example, my file has this:

AAA  
BBB  
CCC  
DDD  
EEE

I w

Answer 1

I benchmarked the following Perl modules:

1. Math::Combinatorics
2. Algorithm::Combinatorics
3. Cmb

Benchmark consisted of doing what the OP asked, combinations of 2 items, but ramping the set of words up to 10,000 instead of just the original 5 requested (AAA BBB CCC DDD EEE).

Test script for Math::Combinatorics

#!/usr/bin/env perl
use strict; use warnings;
use Math::Combinatorics;
my $strings = [qw(AAA BBB CCC DDD EEE) x 2000];
my $iter = new Math::Combinatorics (count => 2, data => $strings);
while (my @c = $iter->next_combination) {
    print "@c\n";
}

This produced ~53,479 combinations per-second.

Test script for Algorithm::Combinatorics

#!/usr/bin/env perl
use strict; use warnings;
use Algorithm::Combinatorics qw(combinations);
my $strings = [qw(AAA BBB CCC DDD EEE) x 2000];
my $iter = combinations($strings, 2);
while (my $c = $iter->next) {
    print "@$c\n";
}

This produced ~861,982 combinations per-second.

Test script for Cmb

#!/usr/bin/env perl
use strict; use warnings;
use Cmb;
my $strings = [qw(AAA BBB CCC DDD EEE) x 2000];
my $cmb = new Cmb { size_min => 2, size_max => 2 };
$cmb->cmb_callback($#$strings + 1, $strings, sub {
    print "@_\n";
    return 0;
});

This produced ~2,940,882 combinations per-second.

But if you just need to print the combinations, Cmb can actually do that even faster than the above.

#!/usr/bin/env perl
use strict; use warnings;
use Cmb;
my $strings = [qw(AAA BBB CCC DDD EEE) x 2000];
my $cmb = new Cmb { size_min => 2, size_max => 2 };
$cmb->cmb($#$strings + 1, $strings);

This produced ~3,333,000 combinations per-second.

Benchmarks were performed using dpv on CentOS Linux release 7.7.1908 (Core) under kernel 3.10.0-1062.1.1.el7.x86_64 x86_64 using Perl 5.16.3 on an Intel(R) Xeon(R) CPU E5-2699 v4 @ 2.20GHz