How can I handle nested looping without nesting foreach statements in Perl?

Question

I have a Perl script which nests foreach loops as seen below. It takes a long time:

#! /usr/bin/perl

use strict;
use warnings;

my @sites = ('a', 'b', 'c');
my @servers = ('A', 'B');
my @data_type = ("X", "Y", "Z");

foreach my $site (@sites) {
    foreach my $server_type (@servers) {
        foreach my $data (@data_type) {
            #statements
        }
    }
}

Nesting foreach statements like this takes a long time and it's hard to read and not very pretty. Can anyone suggest a better way to code this structure using hashes, or some other clever structure?

Answer 1

Use my Set::CrossProduct module, or use Algorithm::Loops. You shouldn't have to create hard-coded, nested structures to deal with these issues. Both of those modules can do it for you for an arbitrary number of arrays.

use Set::CrossProduct;

my @sites = ('a', 'b', 'c');
my @servers = ('A', 'B');
my @data_type = ("X", "Y", "Z");

my $cross = Set::CrossProduct->new( 
    [ \@sites, \@servers, \@data_type ]
    );

while( my $tuple = $cross->get ) {
    print "@$tuple\n";
    }

Not only that, but the cursor gives you ways to move around in the iterator so you don't have to limit yourself to the current combination. You can inspect the previous and next combinations, which might be useful for boundaries (like where the next tuple is a different server).

Watch out for people who want to create all of the combinations in memory. There's no need to do that either.