php无限极分类的实现

    //指定根层级的树状图
    function generateTree($list, $root = 0, $pk = 'id', $pid = 'pid', $child = '_child')
    {
        $tree     = array();
        $packData = array();
        foreach ($list as $data) {
            $packData[$data[$pk]] = $data;
        }
        foreach ($packData as $key => $val) {
            if ($val[$pid] == $root) {
//代表跟节点, 重点一
                $tree[] = &$packData[$key];
            } else {
                //找到其父类,重点二
                $packData[$val[$pid]][$child][] = &$packData[$key];
            }
        }
        return $tree;
    }