Database
[{"_id":"5f5a1c1f6976570001783ab7","date":NumberLong(1590624000),"source":"here"},{"_id":"5f5a1c1f6976570001783ab8","date":NumberLong(1590634000),"source":"here"},{"_id":"5f5a1c1f6976570001783ab9","date":NumberLong(1590634000),"source":"here"},{"_id":"5f5a1c1f6976570001783ab6","date":NumberLong(1590624000),"source":"there"}]
Query
db.collection.aggregate([{"$match":{"source":"here"}},{"$group":{"_id":"$date","count":{"$sum":1}}},{"$project":{"_id":0,"date":"$_id","count":1}}])