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
019 package org.apache.hadoop.mapreduce.lib.aggregate;
020
021 import java.io.IOException;
022
023 import org.apache.hadoop.classification.InterfaceAudience;
024 import org.apache.hadoop.classification.InterfaceStability;
025 import org.apache.hadoop.io.Text;
026 import org.apache.hadoop.io.Writable;
027 import org.apache.hadoop.io.WritableComparable;
028 import org.apache.hadoop.mapreduce.Reducer;
029
030 /**
031 * This class implements the generic reducer of Aggregate.
032 */
033 @InterfaceAudience.Public
034 @InterfaceStability.Stable
035 public 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 }