几行php代码把数据格式化成树形结构

<?php

/**
 * 将数据格式化成树形结构
 * @author Xuefen.Tong
 * @param array $items
 * @return array
 */
function genTree5($items) {
    foreach ($items as $item){
        $items[$item['pid']]['son'][$item['id']] = &$items[$item['id']];
    }
    return isset($items[0]['son']) ? $items[0]['son'] : array();
}

function genTree9($items) {
    $tree = array(); //格式化好的树
    foreach ($items as $item)
        if (isset($items[$item['pid']]))
            $items[$item['pid']]['son'][] = &$items[$item['id']];
        else
            $tree[] = &$items[$item['id']];
    return $tree;
}

// 测试代码：

        $items = array(
            6 => array('id' => 6, 'pid' => 4, 'name' => '香坊区'),
            
            1 => array('id' => 1, 'pid' => 0, 'name' => '江西省'),
            2 => array('id' => 2, 'pid' => 0, 'name' => '黑龙江省'),
            3 => array('id' => 3, 'pid' => 1, 'name' => '南昌市'),
            4 => array('id' => 4, 'pid' => 2, 'name' => '哈尔滨市'),
//            5 => array('id' => 5, 'pid' => 2, 'name' => '鸡西市'),
//
            7 => array('id' => 7, 'pid' => 4, 'name' => '南岗区'),
//            8 => array('id' => 8, 'pid' => 6, 'name' => '和兴路'),
//            9 => array('id' => 9, 'pid' => 7, 'name' => '西大直街'),
//            10 => array('id' => 10, 'pid' => 8, 'name' => '东北林业大学'),
//            11 => array('id' => 11, 'pid' => 9, 'name' => '哈尔滨工业大学'),
//            12 => array('id' => 12, 'pid' => 8, 'name' => '哈尔滨师范大学'),
//            13 => array('id' => 13, 'pid' => 1, 'name' => '赣州市'),
//            14 => array('id' => 14, 'pid' => 13, 'name' => '赣县'),
//            15 => array('id' => 15, 'pid' => 13, 'name' => '于都县'),
//            16 => array('id' => 16, 'pid' => 14, 'name' => '茅店镇'),
//            17 => array('id' => 17, 'pid' => 14, 'name' => '大田乡'),
//            18 => array('id' => 18, 'pid' => 16, 'name' => '义源村'),
//            19 => array('id' => 19, 'pid' => 16, 'name' => '上坝村'),
        );

        echo "<pre>";

        print_r(genTree5($items));