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I am trying to aggregate an events field. I am supposed to find the sum.

Here is a sample of the dataset. 

{ "_id" : ObjectId("582db9b82de1b251ee2d60a9"), "uuid" : "4898009f81a3ee8a", "session_id" : "26102016181211", "project_token" : "5a26b01e-622d-4512-aba4-158651cd0846", "starttime" : ISODate("2016-10-26T23:46:07Z"), "activity_name" : "ProductInfoActivity", "content_id" : 987560, "endtime" : ISODate("2016-10-26T23:48:42Z"), "time_duration" : 86245, "motion" : "running", "timestamp" : "Wed Nov 16 11:44:54 +05:30 2016", "os" : "Android", "events" : [ { "Virality" : 3, "_id" : "Virality" } ] }

So far I have got to this query.

db.pageview.aggregate([{$match:{'project_token':"5a26b01e-622d-4512-aba4-158651cd0846",'content_id':987560}},{'$group':{ _id : '$events._id','total_Virality':{$sum:'$events.Virality'}}}])

It gives me a result as

{ "_id" : [ "Virality" ], "total_Virality" : 0 }
{ "_id" : null, "total_Virality" : 0 }

It is supposed to give me a 3 but it returns 0 instead.

Any help is appreciated.

Improve this question
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  • $unwind before applying grouping. {'$unwind':'$events'} Commented Nov 21, 2016 at 10:26
  • You mean db.pageview.aggregate([{$match:{'project_token':"5a26b01e-622d-4512-aba4-158651cd0846",'content_id':987560}},{'$unwind':'$events'},{'$group':{ '_id' : '$events._id','total_Virality':{$sum:'$events.Virality'}}}]) . It works. You can add it as an answer. Commented Nov 21, 2016 at 10:29
  • nah it's cool. it has been previously answered. I'll have wait for somebody to mark as duplicate. Commented Nov 21, 2016 at 10:30
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