is there a way to leverage the shuffle in Dataset/GroupedDataset so that Iterator[V] in flatMapGroups has a well defined ordering?
is hard for me to see many good use cases for flatMapGroups and mapGroups if you do not have sorting. since spark has a sort based shuffle not exposing this would be a missed opportunity, not unlike SPARK-3655 <https://issues.apache.org/jira/browse/SPARK-3655>. And unlike with RDD where this could be implemented in an external library without too much trouble, i think with Dataset it is hard for a spark "user" to add this functionality.
