count in aggregate mongodb code example

Example 1: mongodb aggregate count

#return the number of documents whose "field" field has a value of A 
query = db.collection.aggregate([{
          "$match": {
            "field": "A"
          }
        },{
          "$count": "number of occurrences"
}])

Example 2: mongo count

db.collection.countDocuments( <query>, <options> )