This works, but not well enough. Needs better handling of undefined values and arranging things in fixed lengths. For example, if there three items and only one has a sort key, but it's sort key asks to be in the second place, then the item specifying spot two should get spot two and all the undefined items should maintain order around it. Funda…

array_sortByKey.php

public function array_sortByKey($arr, $key)
{
    $sort_on_key = function ($a, $b) use ($key) {
        $a[$key] = (isset($a[$key])) ?: null;
        $b[$key] = (isset($b[$key])) ?: null;
        return strnatcmp($a[$key], $b[$key]);
    };
    usort($arr, $sort_on_key);
    return $arr;
}