A package that returns all the combinations and permutations, without repitition, of a given set and subset size. Associative arrays are preserved. Download from: http://pear.php.net/package/Math_Combinatorics/download

combinations.php

require_once 'Math/Combinatorics.php';

$combinatorics = new Math_Combinatorics;
var_dump($combinatorics->combinations(array(
    'one'   => 'a',
    'two'   => 'b',
    'three' => 'c',
    'four'  => 'd',
    ), 3));

permutations.php

require_once 'Math/Combinatorics.php';

$combinatorics = new Math_Combinatorics;
var_dump($combinatorics->permutations(array(
    'one'   => 'a',
    'two'   => 'b',
    'three' => 'c',
    'four'  => 'd',
    ), 3));