PHP: convert object / array to tree structure

build-tree.php

<?php
/*
 * Source: http://goo.gl/p2GybZ
 */
// for object
function buildTree($items) {

    $childs = array();

    foreach($items as $item)
        $childs[$item->parent_id][] = $item;

    foreach($items as $item) if (isset($childs[$item->id]))
        $item->childs = $childs[$item->id];

    return $childs[0];
}
// or array version
function buildTree($items) {

    $childs = array();

    foreach($items as &$item) $childs[$item['parent_id']][] = &$item;
    unset($item);

    foreach($items as &$item) if (isset($childs[$item['id']]))
            $item['childs'] = $childs[$item['id']];

    return $childs[0];
}

// usage:
$tree = buildTree($items);