library/src/main/java/com/datatorrent/lib/statistics/ModeOperator.java

/*
 * Copyright (c) 2013 DataTorrent, Inc. ALL Rights Reserved.
 *
 * Licensed 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.statistics;

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

import com.datatorrent.api.BaseOperator;
import com.datatorrent.api.DefaultInputPort;
import com.datatorrent.api.DefaultOutputPort;
import com.datatorrent.api.annotation.InputPortFieldAnnotation;
import com.datatorrent.api.annotation.OperatorAnnotation;
import com.datatorrent.api.annotation.OutputPortFieldAnnotation;

/**
 * An implementation of BaseOperator that calculates most frequent value occurring in incoming data. <br>
 * <br>
 * <b>Input Port(s) : </b><br>
 * <b>data : </b> Data values input port. <br>
 * <br>
 * <b>Output Port(s) : </b> <br>
 * <b>mode : </b>Mode value output port. <br>
 * <br>
 * <b>StateFull : Yes</b>, value are aggregated over application window. <br>
 * <b>Partitions : No</b>, no will yeild wrong results. <br>
 * <br>
 * @displayName: Mode
 * @category: statistics
 * @tag: numeric, integer, count
 * @since 0.3.4
 */
@OperatorAnnotation(partitionable = false)
public class ModeOperator<V extends Comparable<?>> extends BaseOperator
{
  /**
   * Value/Count map.
   */
  HashMap<V, Integer>   values = new  HashMap<V, Integer>();
  /**
   * Input data port that takes comparable values.
   */
  @InputPortFieldAnnotation(name = "data")
  public final transient DefaultInputPort<V> data = new DefaultInputPort<V>()
  {
    /**
     * Computes sum and count with each tuple
     */
    @Override
    public void process(V tuple)
    {
      if (values.containsKey(tuple)) {
        Integer count = values.remove(tuple);
        values.put(tuple, count+1);
      } else {
        values.put(tuple, 1);
      }
    }
  };
  
  /**
   * Output port that emits most frequent value in incoming data.
   */
  @OutputPortFieldAnnotation(name = "mean")
  public final transient DefaultOutputPort<V> mode = new DefaultOutputPort<V>();
  
  /**
   * Emit mode value.
   */
  @Override
  public void endWindow()
  {
    V modeValue = null;
    int max = 0;
    for (Map.Entry<V, Integer> entry : values.entrySet()) {
      if (entry.getValue() > max) {
        modeValue = entry.getKey();
        max = entry.getValue();
      }
    }
    if (mode != null) {
      mode.emit(modeValue);
    }
  }
}