Sorting an array of arrays by the child array's length?

What's the best way in PHP to sort an array of arrays based on array length?

e.g.

$parent[0] = array(0, 0, 0);
$parent[2] = array("foo", "bar", "b", "a", "z");
$parent[1] = array(4, 2);

$sorted = sort_by_length($parent)

$sorted[0] = array(4, 2);
$sorted[1] = array(0, 0, 0);
$sorted[2] = array("foo", "bar", "b", "a", "z");

From stackoverflow

• What about just using the length as the array key, then doing a ksort? eg:

  function sort_by_length($parent) { 
    foreach($parent as $child) {
     $sorted[count($child)] = $child;
    }
    return ksort($sorted);
  }
  

• This will work:

  function sort_by_length($arrays) {
      $lengths = array_map('count', $arrays);
      asort($lengths);
      $return = array();
      foreach(array_keys($lengths) as $k)
       $return[$k] = $arrays[$k];
      return $return;
  }
  

  Note that this function will preserve the numerical keys. If you want to reset the keys, wrap it in a call to array_values().

• I'm upvoting Peter's but here's another way, I think:

  function cmp($a1, $a2) {
      if (count($a1) == count($a2)) {
          return 0;
      }
      return (count($a1) < count($a2)) ? -1 : 1;
  }
  
  usort($array, "cmp");
  

• Try the usort function:

  function sortByLength( $arr1, $arr2 )
  {
      $c1 = count($arr1);
      $c2 = count($arr2);
  
      return $c1 < $c2 ? -1 : $c1 == $c2 ? 0 : 1;
  }
  
  usort($initial_array,'sortByLength');
  

  edited to respect parameters-by-reference; it's the same answer as @david, anyway