db={"data":[{"_id":ObjectId("611a99100a3322fc1bd8c38b"),"timestamp":ISODate("2021-04-01T00:00:00Z"),"fname":"Tom","city":"United States of America","courses":["c#","asp","node"]},{"_id":ObjectId("611a99340a3322fc1bd8c38c"),"fname":"Harry","city":"Canada","courses":["python","asp","node"]},{"_id":ObjectId("611a99510a3322fc1bd8c38d"),"fname":"Mikky","city":"New Zealand","courses":["python","asp","c++"]},{"_id":ObjectId("611b3e88a60b5002406571c3"),"fname":"Ron","city":"United Kingdom","courses":["python","django","node"]}]}

db.data.aggregate([{$group:{_id:{name:"$name",timestamp:"$timestamp"}}},{$count:"timestamp"}])