001/**
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *     http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018
019package org.apache.hadoop.mapreduce.lib.aggregate;
020
021import java.io.IOException;
022
023import org.apache.hadoop.classification.InterfaceAudience;
024import org.apache.hadoop.classification.InterfaceStability;
025import org.apache.hadoop.io.Text;
026import org.apache.hadoop.io.Writable;
027import org.apache.hadoop.io.WritableComparable;
028import org.apache.hadoop.mapreduce.Reducer;
029
030/**
031 * This class implements the generic reducer of Aggregate.
032 */
033@InterfaceAudience.Public
034@InterfaceStability.Stable
035public class ValueAggregatorReducer<K1 extends WritableComparable<?>,
036                                    V1 extends Writable>
037  extends Reducer<Text, Text, Text, Text> {
038
039  public void setup(Context context) 
040      throws IOException, InterruptedException {
041    ValueAggregatorJobBase.setup(context.getConfiguration());
042  }
043
044  /**
045   * @param key
046   *        the key is expected to be a Text object, whose prefix indicates
047   *        the type of aggregation to aggregate the values. In effect, data
048   *        driven computing is achieved. It is assumed that each aggregator's
049   *        getReport method emits appropriate output for the aggregator. This
050   *        may be further customized.
051   * @param values the values to be aggregated
052   * @param context 
053   */
054  public void reduce(Text key, Iterable<Text> values,
055      Context context) throws IOException, InterruptedException {
056    String keyStr = key.toString();
057    int pos = keyStr.indexOf(ValueAggregatorDescriptor.TYPE_SEPARATOR);
058    String type = keyStr.substring(0, pos);
059    keyStr = keyStr.substring(pos + 
060               ValueAggregatorDescriptor.TYPE_SEPARATOR.length());
061    long uniqCount = context.getConfiguration().
062      getLong(UniqValueCount.MAX_NUM_UNIQUE_VALUES, Long.MAX_VALUE);
063    ValueAggregator aggregator = ValueAggregatorBaseDescriptor
064      .generateValueAggregator(type, uniqCount);
065    for (Text value : values) {
066      aggregator.addNextValue(value);
067    }
068
069    String val = aggregator.getReport();
070    key = new Text(keyStr);
071    context.write(key, new Text(val));
072  }
073}