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 );