From ca9f81e8fcf46bceb032f3bd0efb9f6ed2c25656 Mon Sep 17 00:00:00 2001
From: Mark Hamstra <markhamstra@gmail.com>
Date: Sat, 16 Mar 2013 13:31:01 -0700
Subject: [PATCH] refactor foldByKey to use combineByKey
---
core/src/main/scala/spark/PairRDDFunctions.scala | 14 ++++++++++----
.../main/scala/spark/api/java/JavaPairRDD.scala | 12 +++++++++---
2 files changed, 19 insertions(+), 7 deletions(-)
diff --git a/core/src/main/scala/spark/PairRDDFunctions.scala b/core/src/main/scala/spark/PairRDDFunctions.scala
index ffa6336ceb..e1dde1b497 100644
--- a/core/src/main/scala/spark/PairRDDFunctions.scala
+++ b/core/src/main/scala/spark/PairRDDFunctions.scala
@@ -89,22 +89,28 @@ class PairRDDFunctions[K: ClassManifest, V: ClassManifest](
}
/**
- * Merge the values for each key using an associative function and a neutral "zero value".
+ * Merge the values for each key using an associative function and a neutral "zero value" which may
+ * be added to the result an arbitrary number of times, and must not change the result (e.g., Nil for
+ * list concatenation, 0 for addition, or 1 for multiplication.).
*/
def foldByKey(zeroValue: V, partitioner: Partitioner)(func: (V, V) => V): RDD[(K, V)] = {
- groupByKey(partitioner).mapValues(seq => seq.fold[V](zeroValue)(func))
+ combineByKey[V]({v: V => func(zeroValue, v)}, func, func, partitioner)
}
/**
- * Merge the values for each key using an associative function and a neutral "zero value".
+ * Merge the values for each key using an associative function and a neutral "zero value" which may
+ * be added to the result an arbitrary number of times, and must not change the result (e.g., Nil for
+ * list concatenation, 0 for addition, or 1 for multiplication.).
*/
def foldByKey(zeroValue: V, numPartitions: Int)(func: (V, V) => V): RDD[(K, V)] = {
foldByKey(zeroValue, new HashPartitioner(numPartitions))(func)
}
/**
- * Merge the values for each key using an associative function and a neutral "zero value".
+ * Merge the values for each key using an associative function and a neutral "zero value" which may
+ * be added to the result an arbitrary number of times, and must not change the result (e.g., Nil for
+ * list concatenation, 0 for addition, or 1 for multiplication.).
*/
def foldByKey(zeroValue: V)(func: (V, V) => V): RDD[(K, V)] = {
foldByKey(zeroValue, defaultPartitioner(self))(func)
diff --git a/core/src/main/scala/spark/api/java/JavaPairRDD.scala b/core/src/main/scala/spark/api/java/JavaPairRDD.scala
index 1dc73a3584..49aaabf835 100644
--- a/core/src/main/scala/spark/api/java/JavaPairRDD.scala
+++ b/core/src/main/scala/spark/api/java/JavaPairRDD.scala
@@ -161,19 +161,25 @@ class JavaPairRDD[K, V](val rdd: RDD[(K, V)])(implicit val kManifest: ClassManif
rdd.countByKeyApprox(timeout, confidence).map(mapAsJavaMap)
/**
- * Merge the values for each key using an associative function and a neutral "zero value".
+ * Merge the values for each key using an associative function and a neutral "zero value" which may
+ * be added to the result an arbitrary number of times, and must not change the result (e.g., Nil for
+ * list concatenation, 0 for addition, or 1 for multiplication.).
*/
def foldByKey(zeroValue: V, partitioner: Partitioner, func: JFunction2[V, V, V]): JavaPairRDD[K, V] =
fromRDD(rdd.foldByKey(zeroValue, partitioner)(func))
/**
- * Merge the values for each key using an associative function and a neutral "zero value".
+ * Merge the values for each key using an associative function and a neutral "zero value" which may
+ * be added to the result an arbitrary number of times, and must not change the result (e.g., Nil for
+ * list concatenation, 0 for addition, or 1 for multiplication.).
*/
def foldByKey(zeroValue: V, numPartitions: Int, func: JFunction2[V, V, V]): JavaPairRDD[K, V] =
fromRDD(rdd.foldByKey(zeroValue, numPartitions)(func))
/**
- * Merge the values for each key using an associative function and a neutral "zero value".
+ * Merge the values for each key using an associative function and a neutral "zero value" which may
+ * be added to the result an arbitrary number of times, and must not change the result (e.g., Nil for
+ * list concatenation, 0 for addition, or 1 for multiplication.).
*/
def foldByKey(zeroValue: V, func: JFunction2[V, V, V]): JavaPairRDD[K, V] =
fromRDD(rdd.foldByKey(zeroValue)(func))
--
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