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here's a list of documents:

{_id:1, manufacturer: "Sony", features: ["fast", "sleek", "sexy"]}

{_id:2, manufacturer: "Sony", features: ["lightweight", "sleek"]}

{_id:3, manufacturer: "Sony", features: ["cheap", "fast"]}

{_id:4, manufacturer: "Apple", features: ["fast", "sleek", "usable"]}

{_id:5, manufacturer: "Apple", features: ["lightweight", "sleek", "cheap"]}

{_id:6, manufacturer: "Apple", features: ["fast", "usable", "codecs"]}

I'd like to output to look like:

  "manufacturer": {

    "Sony":3,

    "Apple":3

},

  "features": {

    "fast": 4,

    "cheap": 2,

    "codecs": 1,

    "usable": 2,

    "lightweight": 2,

    "sleek": 3,

    "sexy": 1,

Here's my opinion on how to make this request:

db.coll.aggregate(

  {$count: ["manufacturer", "features"]}

Alternately, I'd be fine with a new group aggregation function, like so:

db.coll.aggregate({

  $group: {

    manufacturer: {$count: "$manufacturer"},

    features: {$count: "$features"}

})

Although this obviously requires that the need to specify an _id be lifted, or accounted for in some way.

is related to

SERVER-12927 Support ROLLUP function in the $group aggregation operator

SERVER-23836 add $count stage to aggregation

Participants:: Asya Kamsky, Backlog - Query Team, Charlie Swanson, Nathan Wells