count of result in aggregate

[Ali hallaji]

Hi,

how to count all result in aggregate?

[Victor Hooi]

Hi Ali,

You can count items in an aggregation using the $group aggregation operator and $sum.

For example, if we have the following documents:

> db.dogs.find()
{ "_id" : ObjectId("539e8c759a349385717251f0"), "name" : "spot" } { "_id" : ObjectId("539e8c759a349385717251f1"), "name" : "fifo" } { "_id" : ObjectId("539e8c759a349385717251f2"), "name" : "spot the second" }

Here is a how to do a simple tally of all documents in this collection:

> db.dogs.aggregate({$group: {_id: "dogs", "count":
{"$sum": 1}
}});
{ "_id" : "dogs", "count" : 3 }

You can put this in a pipeline this with your other aggregation operations. I'd encourage you to read through the aggregation examples on the Zip Code Data Set and User Preference Data. If you get stuck, paste the code you have for your aggregation and somebody can help you debug it.

Please let me know if you have any queries about any of the above.

Regards,

Victor