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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