如何在laravel中聚合mongodb集合数据

Question

我有这样的集合

 {
    "wl_total" : 380,
    "player_id" : 1241,
    "username" : "Robin",
    "hand_id" : 292656,
    "time" : 1429871584
}
{
    "wl_total" : -400,
    "player_id" : 1243,
    "username" : "a",
    "hand_id" : 292656,
    "time" : 1429871584
}

因为两个集合都有相同的hand_id我想在hand_id的基础上聚合这两个集合 我希望结果为

的组合

data=array(
       'hand_id'=>292656,
        'wl_total'=>
                   {
                    0=>380,
                    1=>-400
                   },
         'username'=>
                   {
                    0=>"Robin",
                    1=>"a"
                   },
          "time"=>1429871584
     )