mongo query to aggregate 2 documents for 2 dates

Question

i have following collection...

[{
   "_id":"abcd1234",
    "Date" :{"$date":1430418601000},

    "Count":{
        "hr1":0,
        "hr2":20,
        "hr3":1,
        "hr4":4,
        "hr5":0,
      }
},
{
   "_id":"abcd1234",
   "Date" :{"$date":1430505001000},
   "Count":{
       "hr1":2,
       "hr2":15,
       "hr3":15,
       "hr4":0,
       "hr5":1,
}
}
]

I want to aggregate count for these dates so total count will be like...

{"hr1":2,
 "hr2":35,
 "hr3":16,//......so on
}

Is it possible in mongodb? I don't have much knowledge of mongo, if someone can guide me with this query will be helpful...

Answer 1

Running the following aggregation pipeline should give you the desired result:

db.collection.aggregate([
    {
        "$group": {
            "_id": null,
            "hr1": { "$sum": "$Count.hr1" },
            "hr2": { "$sum": "$Count.hr2" },
            "hr3": { "$sum": "$Count.hr3" },
            "hr4": { "$sum": "$Count.hr4" },
            "hr5": { "$sum": "$Count.hr5" }
        }
    }
])

Specifying an _id value of null will calculate accumulated values for all the input documents as a whole.