Github user cloud-fan commented on a diff in the pull request:
https://github.com/apache/spark/pull/20806#discussion_r174276969
--- Diff: sql/core/src/main/scala/org/apache/spark/sql/Dataset.scala ---
@@ -1658,6 +1659,43 @@ class Dataset[T] private[sql](
def groupByKey[K](func: MapFunction[T, K], encoder: Encoder[K]):
KeyValueGroupedDataset[K, T] =
groupByKey(func.call(_))(encoder)
+
+ /**
+ * Aggregates the elements of this Dataset in a multi-level tree pattern.
+ *
+ * @param depth suggested depth of the tree (default: 2)
+ */
+ private[spark] def treeAggregate[U : Encoder : ClassTag](zeroValue: U)(
+ seqOp: (U, T) => U,
+ combOp: (U, U) => U,
+ depth: Int = 2): U = {
+ require(depth >= 1, s"Depth must be greater than or equal to 1 but got
$depth.")
--- End diff --
why would depth 1 make sense?
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