mongodb - how to find and then aggregate

Question

I have collection that contains documents with below schema. I want to filter/find all documents that contain the gender female and aggregate the sum of brainscore. I tried the

Answer 1

You have to use $match:

db['!all'].aggregate([
  {$match:
    {'GENDER': 'F',
     'DOB':
      { $gte: 19400801,
        $lte: 20131231 } } },
  {$group:
     {_id: "$GENDER",
     totalscore:{ $sum: "$BRAINSCORE"}}}
])

Outputs:

{ "_id" : "F", "totalscore" : 109 }