MongoDB Aggregation: Counting distinct fields

Question

I am trying to write an aggregation to identify accounts that use multiple payment sources. Typical data would be.

{
 account:\"abc\",
 vendor:\"amazon\",
}         


        

Answer 1

An example

db.collection.distinct("example.item").forEach( function(docs) {
    print(docs + "==>>" + db.collection.count({"example.item":docs}))
});

Answer 2

To identify accounts that use multiple payment sources:

1. Use grouping to count data from multiple account records and group the result by account with count
2. Use a match case is to filter only such accounts having more than one payment method

  db.payment_collection.aggregate([ { $group: {"_id":"$account" ,
 "number":{$sum:1}} }, {
                     "$match": {
                         "number": { "$gt": 1 }
                      }
                 } ])

This will work perfectly fine,