Random pairing

function random_pairing($pairs) {
      $out = array();
 
      // Fail if number of items is odd
      $first = array();
      $second = array();
 
      for($i = 0; $i < $pairs * 2; $i++){
 
         $nums[] = $i;
 
      }
 
      shuffle($nums);
 
      $first = array_slice($nums, 0, $pairs);
      $second = array_slice($nums, $pairs, $pairs);
 
      shuffle($second);
 
      return array_combine($first, $second);
  }