Sort multidimensional array with usort by children

Question

I'm working within the CakePHP framework, and have the following multidimensional array that I will need to sort by values. I'm using usort, but cannot figure out how to sort by the children of [ForumPost].

Here's the array:

Array
( 
    [0] => Array
        (
            [ForumPost] => Array
                (
                    [id] => 174
                    [forum_id] => 81
                    [user_id] => 39
                    [title] => A test post
    [1] => Array
        (
            [ForumPost] => Array
                (
                    [id] => 64
                    [forum_id] => 208
                    [user_id] => 36
                    [title] => B test post
... etc

My function and call are:

usort($array, array("ForumSearchesController", "cmp"));

function cmp($a, $b) {
    return $a['ForumPost']['title'] - $b['ForumPost']['title'];
}

Answer 1

You cannot simply subtract titles (strings) from each other and expect a meaningful result. The equivalent for strings is calling the function strcmp:

function cmp($a, $b) {
    return strcmp($a['ForumPost']['title'], $b['ForumPost']['title']);
}