flatten.php

/**
 * Recursively flattens an array
 *
 * @param array $arr
 *
 * @return array
 */
function flatten(array $arr)
{
    $recursiveIterator = new RecursiveArrayIterator($arr);
    $recursiveIteratorIterator = new RecursiveIteratorIterator($recursiveIterator);

    return iterator_to_array($recursiveIteratorIterator, FALSE);
}