org.apache.hadoop.hive.contrib.mr.Reducer Maven / Gradle / Ivy

/**
 * 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.hive.contrib.mr;

import java.util.Iterator;

/**
 * Simple reducer interface.
 */
public interface Reducer {
  /**
   * Reduce.
   * 
   * Note that it is assumed that the key is the first column. Additionally, the
   * key will be repeated as the first column in the records[] array.
   * 
   * @param key
   *          key (first column) for this set of records.
   * @param records
   *          Iterator of records for this key. Note that the first column of
   *          record will also be the key.
   * @param output
   * @throws Exception
   */
  void reduce(String key, Iterator records, Output output)
      throws Exception;
}