Take an array of strings and sort them by the third character of each strings

function sort_string_array($string_array) {
  usort($string_array, function($a, $b) {
    if ($a[2] == $b[2]) {
      return 0;
    }
    return ($a[2] < $b[2]) ? -1 : 1;
  });
  return $string_array;
}