/** * 把返回的数据集转换成Tree * @param array $list 要转换的数据集 * @param string $pid parent标记字段 * @param string $level level标记字段 * @return array * @author 麦当苗儿 
     
       */function list_to_tree($list, $pk='id', $pid = 'pid', $child = '_child', $root = 0) {    // 创建Tree    $tree = array();    if(is_array($list)) {        // 创建基于主键的数组引用        $refer = array();        foreach ($list as $key => $data) {            $refer[$data[$pk]] =& $list[$key];        }        foreach ($list as $key => $data) {            // 判断是否存在parent            $parentId =  $data[$pid];            if ($root == $parentId) {                $tree[] =& $list[$key];            }else{                if (isset($refer[$parentId])) {                    $parent =& $refer[$parentId];                    $parent[$child][] =& $list[$key];                }            }        }    }    return $tree;}/** * 将list_to_tree的树还原成列表 * @param  array $tree  原来的树 * @param  string $child 孩子节点的键 * @param  string $order 排序显示的键，一般是主键 升序排列 * @param  array  $list  过渡用的中间数组， * @return array        返回排过序的列表数组 * @author yangweijie 
      
        */function tree_to_list($tree, $child = '_child', $order='id', &$list = array()){    if(is_array($tree)) {        $refer = array();        foreach ($tree as $key => $value) {            $reffer = $value;            if(isset($reffer[$child])){                unset($reffer[$child]);                tree_to_list($value[$child], $child, $order, $list);            }            $list[] = $reffer;        }        $list = list_sort_by($list, $order, $sortby='asc');    }    return $list;}