MongoDB Aggregation: Counting distinct fields -

i trying write aggregation identify accounts use multiple payment sources. typical data be.

{  account:"abc",  vendor:"amazon", }  ... {  account:"abc",  vendor:"overstock", } 

now, i'd produce list of accounts similar this

{  account:"abc",  vendorcount:2 } 

how write in mongo's aggregation framework

i figured out using $addtoset , $unwind operators.

mongodb aggregation count array/set size

db.collection.aggregate([ {     $group: { _id: { account: '$account' }, vendors: { $addtoset: '$vendor'} } }, {     $unwind:"$vendors" }, {     $group: { _id: "$_id", vendorcount: { $sum:1} } } ]); 

hope helps someone