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,
     ),

 );

 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);