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?

http://www.merriampark.com/comb.htm (dead link)

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