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

I do not see why somebody would have to use $group twice

db.t2.aggregate([ { $group: {"_id":"$account" , "number":{$sum:1}} } ])

This will work perfectly fine.