I got zero marks in the first assignment because Yifang Sun did not mention Spark is running on parallel. That means a code that seems correct on a single thread (which is the COMP9021 style), could have a different result on Spark. This lecturer is terrible and irresponsible I would like to say since a lot of the contents taught by him were wrong. Worse still, in the final exam, he asked students the issue in assignment 1 which led to almost 50 students got zero marks, though the associated answer had not been taught in the lecture at all!! Be careful of this lecturer!!