php array combination

Question

I want to generate all combination of length r from a set [0...(n-1)]

So the output should be like this (n = 6 r = 2)

$res = array(array(0,1),array(0,2),         


        

Answer 1

Since you need an undefined number of loops, you will need to do it recursively:

function permutation($select, $max) {
    if ($select === 1) {
        $result = range(0, $max);
        foreach ($result as &$entry) {
            $entry = array($entry);
        }
        return $result;
    }
    $result = array();
    $previous = permutation($select - 1, $max - 1);
    foreach ($previous as $entry) {
        $last = end($entry);
        for ($i = $last + 1; $i <= $max; $i++) {
            $result[] = array_merge($entry, array($i));
        }
    }
    return $result;
}