A reader, e.g. Mr. Wayne Zhang, of my previous post (https://statcompute.wordpress.com/2018/09/03/playing-map-and-reduce-in-r-by-group-calculation) made a good comment that “Why not use directly either Spark or H2O to derive such computations without involving detailed map/reduce”. Although Spark is not as flexible as R in the statistical computation (in my opinion), it does have advantages for munging large-size data …