Github user mengxr commented on a diff in the pull request:
https://github.com/apache/spark/pull/5075#discussion_r26616791
--- Diff: core/src/main/scala/org/apache/spark/rdd/PairRDDFunctions.scala
---
@@ -163,6 +163,38 @@ class PairRDDFunctions[K, V](self: RDD[(K, V)])
}
/**
+ * Returns the top k (largest) elements for each key from this RDD as
defined by the specified
+ * implicit Ordering[T]. This does the opposite of [[takeOrderedByKey]].
+ *
+ * @param num k, the number of top elements to return
+ * @param ord the implicit ordering for T
+ * @return an RDD that contains the top k values for each key
+ */
+ def topByKey(num: Int)(implicit ord: Ordering[V]): RDD[(K, Array[V])] =
+ takeOrderedByKey(num)(ord.reverse)
+
+ /**
+ * Returns the first k (smallest) elements for each key from this RDD as
defined by the specified
+ * implicit Ordering[T] and maintains the ordering. This does the
opposite of [[topByKey]].
+ *
+ * @param num k, the number of elements to return
+ * @param ord the implicit ordering for T
+ * @return an RDD that contains the smallest k values for each key
+ */
+ def takeOrderedByKey(num: Int)(implicit ord: Ordering[V]): RDD[(K,
Array[V])] = {
--- End diff --
I think having `topByKey` should be sufficient. Users can reverse the order
easily. @rxin
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