php f3 framework use aggregation framework pipelin

I want to sue aggregation framework pipeline with mongo mapper in the transaction table, the result should be something like this: Suppose I have 7000 transactions in a collection with status 1,2,3,4 (1=pending, 2=confirmed, 3=decline, 4=claimed)

Data Representation:

Pending Count | Confirmed Count | Decline Count | Claimed Count
 4000                 2000            1000          0

1. The issue is I'm not sure which field should be used for the key in the group.

My code is returning me all records which match the criteria.

please have a look at my code:

$filters = array('dateCreated'=>array(
                            '$gte'=>'2015-01-01', 
                            '$lte'=>'2017-05-15'
                    ));

 $group = [
              'keys' =>['userId'=>1],
              'initial' => ['pendingCount'=>0, 'confirmedCount'=>0, 'declineCount'=>0, 'claimedCount'=>0],
              'reduce'=>'
                      function(obj, result){

                        switch(result.status){
                            case 1:
                                result.pendingCount++;
                                break;

                            case 2:
                                result.confirmedCount++;
                                break;                          

                            case 3:
                                result.declineCount++;
                                break;
                            case 4:
                                result.claimedCount++;
                                break;

                        }
                      }
                        ',
              'finalize'=>'function(result){}'
        ];

 $data =  $this->mapper->find($filter, ['group'=>$group]);
 echo "data<pre>";
 print_r($data);

Output:

Here you see it returning me more than one docments but I just want one record for all transaction, may be key userId should be replaced something 'null`

Array ( [0] => Array ( [_id] => MongoId Object ( [$id] => 591a8f5bb06b243d0262d0a1 )

        [userId] => 
        [pendingCount] => 0
        [confirmedCount] => 0
        [declineCount] => 0
        [claimedCount] =>0
    )

[1] => Array
    (
        [_id] => MongoId Object
            (
                [$id] => 591a8f5bb06b243d0262d0a2
            )

        [userId] => 
        [pendingCount] => 0
        [confirmedCount] => 0
        [declineCount] => 0
        [claimedCount] =>0
    )

[2] => Array
    (
        [_id] => MongoId Object
            (
                [$id] => 591a8f5bb06b243d0262d0a3
            )

        [userId] => 38730976
        [pendingCount] => 0
        [confirmedCount] => 0
        [declineCount] => 0
        [claimedCount] =>0
    )

[3] => Array
    (
        [_id] => MongoId Object
            (
                [$id] => 591a8f5bb06b243d0262d0a4
            )

        [userId] => 64920
        [pendingCount] => 0
        [confirmedCount] => 0
        [declineCount] => 0
        [claimedCount] =>0
    )

....

You're grouping by userId so you get one row per userId. Just pass an empty keys array to aggregate data against all records. Also there's a typo in your reducing function: it should be obj.status:

$group = [
  'keys' =>[],
  'initial' => ['pendingCount'=>0, 'confirmedCount'=>0, 'declineCount'=>0],
  'reduce'=>'
    function(obj, result){
      switch(obj.status){
        // etc.
      }
    }
  ',
  'finalize'=>'function(result){}'
];