Github user marmbrus commented on a diff in the pull request:
https://github.com/apache/spark/pull/9628#discussion_r44583721
--- Diff: sql/core/src/main/scala/org/apache/spark/sql/GroupedDataset.scala
---
@@ -127,15 +125,26 @@ class GroupedDataset[K, T] private[sql](
*/
def map[U : Encoder](f: (K, Iterator[T]) => U): Dataset[U] = {
val func = (key: K, it: Iterator[T]) => Iterator(f(key, it))
- new Dataset[U](
- sqlContext,
- MapGroups(func, groupingAttributes, logicalPlan))
+ flatMap(func)
}
def map[U](f: MapGroupFunction[K, T, U], encoder: Encoder[U]):
Dataset[U] = {
map((key, data) => f.call(key, data.asJava))(encoder)
}
+ /**
+ * Reduces the elements of each group of data using the specified binary
function.
+ * The given function must be commutative and associative or the result
may be non-deterministic.
+ */
+ def reduce(f: (T, T) => T): Dataset[(K, T)] = {
+ val func = (key: K, it: Iterator[T]) => Iterator(key -> it.reduce(f))
+ flatMap(func)(ExpressionEncoder.tuple(kEnc, tEnc))
--- End diff --
I'm going to pick this up.
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