PHP Find All (somewhat) Unique Combinations of an Array

Question

I\'ve been looking at PHP array permutation / combination questions all day.. and still can\'t figure it out :/

If I have an array like:

20 //key bei         


        

Answer 1

The pear package Math_Combinatorics makes this kind of problem fairly easy. It takes relatively little code, it's simple and straightforward, and it's pretty easy to read.

$ cat code/php/test.php
combinations($input, 3);
for ($i = 0; $i < count($combinations); $i++) {
  $vals = array_values($combinations[$i]);
  $s = implode($vals, ", ");
  print $s . "\n";
}
?>

$ php code/php/test.php
20, 20, 22
20, 20, 24
20, 22, 24
20, 22, 24

If I had to package this as a function, I'd do something like this.

function combinations($arr, $num_at_a_time) 
{
    include_once 'Math/Combinatorics.php';

    if (count($arr) < $num_at_a_time) {
        $arr_count = count($arr);
        trigger_error(
            "Cannot take $arr_count elements $num_at_a_time " 
            ."at a time.", E_USER_ERROR
        );
    }

    $c = new Math_Combinatorics;
    $combinations = $c->combinations($arr, $num_at_a_time);

    $return = array();
    for ($i = 0; $i < count($combinations); $i++) {
        $values = array_values($combinations[$i]);
        $return[$i] = $values;
    }
    return $return;
}

That will return an array of arrays. To get the text . . .

20, 20, 22
20, 20, 24
20, 22, 24
20, 22, 24