code: /**
   * 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.hadoop.fs.dfsioe;
  
  import java.io.IOException;
  import java.util.Iterator;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.apache.hadoop.io.Text;
  import org.apache.hadoop.mapred.MapReduceBase;
  import org.apache.hadoop.mapred.OutputCollector;
  import org.apache.hadoop.mapred.Reducer;
  import org.apache.hadoop.mapred.Reporter;
  
  /**
   * Reducer that accumulates values based on their type.
   * <p>
   * The type is specified in the key part of the key-value pair 
   * as a prefix to the key in the following way
   * <p>
   * <tt>type:key</tt>
   * <p>
   * The values are accumulated according to the types:
   * <ul>
   * <li><tt>s:</tt> - string, concatenate</li>
   * <li><tt>f:</tt> - float, summ</li>
   * <li><tt>l:</tt> - long, summ</li>
   * </ul>
   * 
   */
  public class AccumulatingReducer extends MapReduceBase
      implements Reducer<Text, Text, Text, Text> {
    private static final Log LOG = LogFactory.getLog(AccumulatingReducer.class);
    
    protected String hostName;
    
    public AccumulatingReducer () {
      LOG.info("Starting AccumulatingReducer !!!");
      try {
        hostName = java.net.InetAddress.getLocalHost().getHostName();
      } catch(Exception e) {
        hostName = "localhost";
      }
      LOG.info("Starting AccumulatingReducer on " + hostName);
    }
    
    public void reduce(Text key, 
                       Iterator<Text> values,
                       OutputCollector<Text, Text> output, 
                       Reporter reporter
                       ) throws IOException {
      String field = key.toString();
  
      reporter.setStatus("starting " + field + " ::host = " + hostName);
  
      // concatenate strings
      if (field.startsWith("s:") || field.startsWith("g:")) {
        String sSum = "";
        while (values.hasNext())
          sSum += values.next().toString() + ";";
        output.collect(key, new Text(sSum));
        reporter.setStatus("finished " + field + " ::host = " + hostName);
        return;
      }
      // sum long values
      if (field.startsWith("f:")) {
        float fSum = 0;
        while (values.hasNext())
          fSum += Float.parseFloat(values.next().toString());
        output.collect(key, new Text(String.valueOf(fSum)));
        reporter.setStatus("finished " + field + " ::host = " + hostName);
        return;
      }
      // sum long values
      if (field.startsWith("l:")) {
        long lSum = 0;
        while (values.hasNext()) {
          lSum += Long.parseLong(values.next().toString());
        }
        output.collect(key, new Text(String.valueOf(lSum)));
      }
      reporter.setStatus("finished " + field + " ::host = " + hostName);
    }
  }
  