algorithm that will take numbers or words and find all possible combinations

Question

I am looking for an algorithm that will take numbers or words and find all possible variations of them together and also let me define how many values to look for together.

Example lets say the string or array is:
cat
dog
fish

then the results for a value of 2 could be:
cat dog
cat fish
dog cat
dog fish
fish cat
fish dog

SO the results from the set of 3 items are 6 possible variations of it at 2 results matching
with 3 results matching it would be:

cat dog fish
cat fish dog
dog cat fish
dog fish cat
fish cat dog
fish dog cat
...probably more options even

I have found a link on Stackoverflow to this example that does this but it is in javascript, I am wondering if anyone knows how to do this in PHP maybe there is something already built?

javascript version here

Answer 1

Take a look at http://pear.php.net/package/Math_Combinatorics

<?php
require_once 'Math/Combinatorics.php';
$words = array('cat', 'dog', 'fish');
$combinatorics = new Math_Combinatorics;
foreach($combinatorics->permutations($words, 2) as $p) {
  echo join(' ', $p), "\n"; 
}

prints

cat dog
dog cat
cat fish
fish cat
dog fish
fish dog