Mongodb aggregate (count) on multiple fields simultaneously

Question

I\'ve got documents that look like this:

{
    \"_id\" : \"someuniqueeventid\",
    \"event\" : \"event_type_1\",
    \"date\" : ISODate(\"2014-01-14T00:00:0         


        

Answer 1

With MongoDb 3.4.4 and newer, you can leverage the use of $arrayToObject operator to get the counts. You would need to run the following aggregate pipeline:

db.data.aggregate([
    { 
        "$group": {
            "_id": {
                "event": "$event",
                "day": { "$substr": [ { "$dayOfWeek": "$date" }, 0, -1 ] }
            },
            "count": { "$sum": 1 }
        }
    },
    { 
        "$group": {
            "_id": "$_id.event",
            "counts": {
                "$push": {
                    "k": "$_id.day",
                    "v": "$count"
                }
            }
        }
    },
    { 
        "$project": {
            "counts": { "$arrayToObject": "$counts" }
        } 
    }    
])