php 合并一个二维数组相同项,数量则相加

$arr = array(
    array(
       'user_id' => 100,
       'goods_id' => 10,
       'number' => 1,
    ),
    array(
       'user_id' => 100,
       'goods_id' => 10,
       'number' => 2,
    ),
    array(
       'user_id' => 100,
       'goods_id' => 10,
       'number' => 2,
    ),
    array(
       'user_id' => 100,
       'goods_id' => 10,
       'number' => 2,
    ),
);
理想结果:
$arr = array(
    array(
        'user_id'=> 100,
        'goods_id' => 10,
        'number' => 7,
    ),

);

 

$item=array();

foreach($arr as $k=>$v){

    if(!isset($item[$v['user_id']])){

        $item[$v['user_id']]=$v;

    }else{

        $item[$v['user_id']]['number']+=$v['number'];

    }

}

print_r($item);