db={"collection":[{"_id":ObjectId("6138ef0a00895c22c6cd3b68"),},],"community_stats":[{_id:ObjectId("613d42f20e8023815b8f0ad3"),community:ObjectId("6138ef0a00895c22c6cd3b68"),data:1,date:ISODate("2021-09-11T23:59:46.998Z")},{_id:ObjectId("613b784e564ee6ad3e2dbb14"),community:ObjectId("6138ef0a00895c22c6cd3b68"),data:2,date:ISODate("2021-09-10T15:22:54.764Z")},{_id:ObjectId("6139f9487e4c964ef9dafd11"),community:ObjectId("6138ef0a00895c22c6cd3b68"),data:3,date:ISODate("2021-09-09T12:08:40.198Z")},{_id:ObjectId("6139f6eac570e66aa60a8b5f"),community:ObjectId("6138ef0a00895c22c6cd3b68"),data:4,date:ISODate("2021-09-09T11:58:34.463Z")}]}

db.collection.aggregate([{$lookup:{from:"community_stats",as:"stats",let:{id:"$_id"},pipeline:[{$match:{$expr:{$eq:["$community","$$id"]}}},{$group:{_id:{year:{"$year":"$date"},month:{"$month":"$date"},day:{"$dayOfMonth":"$date"},},first:{$first:"$$ROOT"}}},{"$replaceRoot":{"newRoot":"$first"}},{$sort:{date:-1}},{$limit:5}]}}])