Convert a PHP multi-dimensional array to a leaf-only array with full-depth array keys

get_leafs.php

<?php

function get_leafs( $array ) {

    $leafs = array();

    if ( ! is_array( $array ) ) {
        return $leafs;
    }

    $array_iterator = new RecursiveArrayIterator( $array );
    $iterator_iterator = new RecursiveIteratorIterator( $array_iterator, RecursiveIteratorIterator::LEAVES_ONLY );
    foreach ( $iterator_iterator as $key => $value ) {
        $keys = array();
        for ( $i = 0; $i < $iterator_iterator->getDepth(); $i++ ) {
            $keys[] = $iterator_iterator->getSubIterator( $i )->key();
        }
        $keys[] = $key;
        $leaf_key = implode( ' ', $keys );

        $leafs[ $leaf_key ] = $value;
    }

    return $leafs;
}