Github user linbojin commented on a diff in the pull request: https://github.com/apache/spark/pull/16276#discussion_r92546374 --- Diff: core/src/main/scala/org/apache/spark/rdd/RDD.scala --- @@ -381,6 +381,14 @@ abstract class RDD[T: ClassTag]( } /** + * Return a new RDD by flattening all elements from RDD with traversable elements + */ + def flatten[U: ClassTag](implicit asTraversable: T => TraversableOnce[U]): RDD[U] = withScope { --- End diff -- Hi @srowen, thx for your suggestion. I have one way to use scala flatMap as follows: ``` def flatten[U: ClassTag](implicit asTraversable: T => TraversableOnce[U]): RDD[U] = withScope { val f = (x: T) => asTraversable(x) val cleanF = sc.clean(f) new MapPartitionsRDD[U, T](this, (context, pid, iter) => iter.flatMap(f)) } ``` Or i implement the logic by myself: ``` def flatten[U: ClassTag](implicit asTraversable: T => TraversableOnce[U]): RDD[U] = withScope { new MapPartitionsRDD[U, T](this, (context, pid, iter) => new Iterator[U] { private val empty = Iterator.empty private var cur: Iterator[U] = empty private def nextCur() { cur = asTraversable(iter.next).toIterator } def hasNext: Boolean = { while (!cur.hasNext) { if (!iter.hasNext) return false nextCur() } true } def next(): U = (if (hasNext) cur else empty).next() }) } ``` ref: https://github.com/scala/scala/blob/v2.11.8/src/library/scala/collection/Iterator.scala#L432 Which one do you think is better?
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