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");

Answer

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().