Database
[{"timestamp":ISODate("2024-01-01T00:00:00Z"),"schema":"1.0.0","value":3},{"timestamp":ISODate("2024-01-01T01:00:00Z"),"schema":"1.2.0","value":-10}]
Query
db.collection.aggregate([{"$group":{"_id":{"bucket":{$toDate:{$subtract:[{$toLong:"$timestamp"},{$mod:[{$toLong:"$timestamp"},86400000]}]}}},"raw":{$push:{values:"$$ROOT"}}}},{"$project":{"_id":0,"bucket":"$_id.bucket","value":{$reduce:{input:"$raw.values",initialValue:{$first:"$raw.values"},in:{$cond:{if:{$gte:[{"$abs":"$$value.value"},{"$abs":"$$this.value"}]},then:"$$value",else:"$$this"}}}}}}])