树应用实现-无限极分类（引用&递归）

$items = array(
    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'),
    6 => array('id' => 6, 'pid' => 4, 'name' => '香坊区'),
    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'),
);

/**
*TODO:通过引用方式实现无限极分类
*    
*/
function tree_Classify1($items){
    $tree=array();
    $packData=array();
    foreach ($items as  $data) {
        $packData[$data['id']] = $data;
    }
    foreach ($packData as $key =>$val){     
        if($val['pid']==0){//代表跟节点       
            $tree[]=& $packData[$key];
        }else{
            //找到其父类
            $packData[$val['pid']]['son'][]=& $packData[$key];
        }
    }
    return $tree;
}

/**
*TODO:通过递归方式实现无限极分类
*      
*/
function tree_Classify2($items,$child='_child',$root = 0){
    $tree=array();
    foreach($items as $key=> $val){

        if($val['pid']==0){
            //获取当前$pid所有子类 
                unset($items[$key]);
                if(! empty($items)){
                    $child=make_tree1($items,$child,$val['id']);
                    if(!empty($child)){
                        $val['_child']=$child;
                    }                   
                }              
                $tree[]=$val; 
        }
    }   
    return $tree;
}

echo "
";
print_r(make_tree1($items,$child='_child',$root=0));