content: /**
   * 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 com.aliyun.odps.mapred.example.local.lib.aggregate;
  
  import java.io.IOException;
  import java.util.Iterator;
  
  import com.aliyun.odps.data.Record;
  import com.aliyun.odps.mapred.ReducerBase;
  
  /**
   * This class implements the generic reducer of Aggregate.
   */
  public class ValueAggregatorReducer extends ReducerBase {
  
    private Record result = null;
  
    @Override
    public void setup(TaskContext context) throws IOException {
      result = context.createOutputRecord();
    }
  
    /**
     * @param key
     *     the key is expected to be a Text object, whose prefix indicates
     *     the type of aggregation to aggregate the values. In effect, data
     *     driven computing is achieved. It is assumed that each aggregator's
     *     getReport method emits appropriate output for the aggregator. This
     *     may be further customiized.
     * @value the values to be aggregated
     */
    @Override
    public void reduce(Record key, Iterator<Record> values, TaskContext context)
        throws IOException {
      String keyStr = key.get(0).toString();
      int pos = keyStr.indexOf(ValueAggregatorDescriptor.TYPE_SEPARATOR);
      String type = keyStr.substring(0, pos);
      keyStr = keyStr.substring(pos
                                + ValueAggregatorDescriptor.TYPE_SEPARATOR.length());
  
      ValueAggregator aggregator = ValueAggregatorBaseDescriptor
          .generateValueAggregator(type);
      while (values.hasNext()) {
        Record val = values.next();
        aggregator.addNextValue(val.get(0).toString());
      }
  
      String val = aggregator.getReport();
  
      result.set(0, keyStr);
      result.set(1, val);
      context.write(result);
    }
  
  }
  