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Java > Open Source Codes > net > nutch > mapReduce > Reducer


1 /* Copyright (c) 2005 The Nutch Organization. All rights reserved. */
2 /* Use subject to the conditions in http://www.nutch.org/LICENSE.txt. */
3
4 package net.nutch.mapReduce;
5
6 import java.io.IOException JavaDoc;
7
8 import java.util.Iterator JavaDoc;
9
10 import net.nutch.io.Writable;
11 import net.nutch.io.WritableComparable;
12
13 /** Reduces a set of intermediate values which share a key to a smaller set of
14  * values. Input values are the grouped output of a {@link Mapper}. */
15 public interface Reducer {
16   /** Combines values for a given key. Output values must be of the same type
17    * as input values. Input keys must not be altered. Typically all values
18    * are combined into zero or one value. Output pairs are collected with
19    * calls to {@link OutputCollector#collect(WritableComparable,Writable)}.
20    *
21    * @param key the key
22    * @param values the values to combine
23    * @param output to collect combined values
24    */
25   void reduce(WritableComparable key, Iterator JavaDoc values, OutputCollector output)
26     throws IOException JavaDoc;
27 }
28
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