PHP树形列表互相转换函数

function list_to_tree($list, $root = 0,$pk = 'id', $pid = 'pid', $child = '_child') {
	// 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
			$parentId=0;
			if(isset($data[$pid])){
				$parentId =$data[$pid] ;
			}
			if ($root == $parentId) {
				$tree[] = &$list[$key];
			} else {
				if (isset($refer[$parentId])) {
					$parent = &$refer[$parentId];
					$parent[$child][] = &$list[$key];
				} 
			}
		} 
	}
	return $tree;
}

function tree_to_list($tree, $level = 0,$pk = 'id', $pid = 'pid', $child = '_child'){
	$list = array();
	if (is_array($tree)){
		foreach($tree as $val) {
			$val['level']=$level;
			$child=$val['_child'];
			if(isset($child)){
				if (is_array($child)){
					unset($val['_child']);
					$list=$val;
					$list = array_merge($list, tree_to_list($child,$level+1));
				}
			}else{
				$list=$val;
			}
		}
		return $list;
	}
}