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/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.spark
import java.util.{HashMap => JHashMap}
import scala.collection.JavaConversions._
/** A set of functions used to aggregate data.
*
* @param createCombiner function to create the initial value of the aggregation.
* @param mergeValue function to merge a new value into the aggregation result.
* @param mergeCombiners function to merge outputs from multiple mergeValue function.
*/
case class Aggregator[K, V, C] (
createCombiner: V => C,
mergeValue: (C, V) => C,
mergeCombiners: (C, C) => C) {
def combineValuesByKey(iter: Iterator[_ <: Product2[K, V]]) : Iterator[(K, C)] = {
val combiners = new JHashMap[K, C]
for (kv <- iter) {
val oldC = combiners.get(kv._1)
if (oldC == null) {
combiners.put(kv._1, createCombiner(kv._2))
} else {
combiners.put(kv._1, mergeValue(oldC, kv._2))
}
}
combiners.iterator
}
def combineCombinersByKey(iter: Iterator[(K, C)]) : Iterator[(K, C)] = {
val combiners = new JHashMap[K, C]
iter.foreach { case(k, c) =>
val oldC = combiners.get(k)
if (oldC == null) {
combiners.put(k, c)
} else {
combiners.put(k, mergeCombiners(oldC, c))
}
}
combiners.iterator
}
}
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