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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 org.apache.spark.util.AppendOnlyMap
/**
* 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 AppendOnlyMap[K, C]
var kv: Product2[K, V] = null
val update = (hadValue: Boolean, oldValue: C) => {
if (hadValue) mergeValue(oldValue, kv._2) else createCombiner(kv._2)
}
while (iter.hasNext) {
kv = iter.next()
combiners.changeValue(kv._1, update)
}
combiners.iterator
}
def combineCombinersByKey(iter: Iterator[(K, C)]) : Iterator[(K, C)] = {
val combiners = new AppendOnlyMap[K, C]
var kc: (K, C) = null
val update = (hadValue: Boolean, oldValue: C) => {
if (hadValue) mergeCombiners(oldValue, kc._2) else kc._2
}
while (iter.hasNext) {
kc = iter.next()
combiners.changeValue(kc._1, update)
}
combiners.iterator
}
}
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