Database
[{"_id":1,"symbol":"AUDHKD","digits":5,"times":{"event_ts_utc":ISODate("2021-10-17T23:59:59.405Z")},"prices":{"bid":5.76648,"ask":5.76848}},{"_id":2,"symbol":"AUDSGD","digits":5,"times":{"event_ts_utc":ISODate("2021-10-17T23:59:59.406Z")},"prices":{"bid":0.99932,"ask":1.00032}},{"_id":3,"symbol":"AUDSGD","digits":5,"times":{"event_ts_utc":ISODate("2021-10-17T23:59:59.618Z")},"prices":{"bid":0.99932,"ask":1.00132}},{"_id":4,"symbol":"AUDHKD","digits":5,"times":{"event_ts_utc":ISODate("2021-10-17T23:59:59.720Z")},"prices":{"bid":5.76648,"ask":5.76878}}]
Query
db.collection.aggregate([{"$match":{"times.event_ts_utc":{$lt:ISODate("2021-10-18")}}},{$sort:{"times.event_ts_utc":-1}},{$group:{_id:"$symbol",latest:{$first:"$$ROOT"}}},{"$replaceRoot":{"newRoot":"$latest"}}])