Mongo count occurrences of each value for a set of documents

You can get result (not in your required format) via aggregation

db.collection.aggregate(
   {$group : { _id : '$user', count : {$sum : 1}}}
).result

the output for your sample documents is:

"0" : {
    "_id" : "2",
    "count" : 1
},
"1" : {
    "_id" : "3",
    "count" : 1
},
"2" : {
    "_id" : "1",
    "count" : 2
}

For anyone reading this in Jan 2019 the accepted answer does not currently work in Robo3T (returns a pipeline.length - 1 error).

You must:

a) wrap the query in a set of square brackets []

b) remove .result from the end

https://github.com/Studio3T/robomongo/issues/1519#issuecomment-441348191

Here's an update to the accepted answer by @disposer that works for me in Robo3T.

db.getCollection('collectionName').aggregate(
    [ {$group : { _id : '$user', count : {$sum : 1}}} ]
)

Related