library/src/main/java/com/datatorrent/lib/util/UnifierHashMapSumKeys.java

/**
 * 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.datatorrent.lib.util;

import java.util.HashMap;
import java.util.Map;

import com.datatorrent.api.Context.OperatorContext;
import com.datatorrent.api.DefaultOutputPort;
import com.datatorrent.api.Operator.Unifier;

/**
 * This unifier consumes hash maps whose keys are objects and whose values are numbers. 
 * The values for each key are summed and emitted in a hash map at the end of each application window.
 * <p>
 * This unifier uses round robin partitioning.
 * </p>
 * @displayName Unifier Hash Map Sum Keys
 * @category Algorithmic
 * @tags numeric, key value
 * @since 0.3.2
 */
public class UnifierHashMapSumKeys<K, V extends Number> extends BaseNumberKeyValueOperator<K,V> implements Unifier<HashMap<K, V>>
{
  public HashMap<K, Double> mergedTuple = new HashMap<K, Double>();
  /**
   * This is the output port which emits key value pairs which map keys to sums.
   */
  public final transient DefaultOutputPort<HashMap<K, V>> mergedport = new DefaultOutputPort<HashMap<K, V>>();

  @Override
  public void process(HashMap<K, V> tuple)
  {
    for (Map.Entry<K, V> e: tuple.entrySet()) {
      Double val = mergedTuple.get(e.getKey());
      if (val == null) {
        mergedTuple.put(e.getKey(), e.getValue().doubleValue());
      } else {
        val += e.getValue().doubleValue();
        mergedTuple.put(e.getKey(), val);
      }
    }
  }

  /**
   * emits mergedTuple on mergedport if it is not empty
   */
  @Override
  public void endWindow()
  {
    if (!mergedTuple.isEmpty()) {
      HashMap<K, V> stuples = new HashMap<K, V>();
      for (Map.Entry<K, Double> e: mergedTuple.entrySet()) {
        stuples.put(e.getKey(), getValue(e.getValue()));
      }
      mergedport.emit(stuples);
      mergedTuple = new HashMap<K, Double>();
    }
  }

  /**
   * a no-op
   * @param context
   */
  @Override
  public void setup(OperatorContext context)
  {
  }

  /**
   * a noop
   */
  @Override
  public void teardown()
  {
  }
}