com.datatorrent.lib.algo.FirstN Maven / Gradle / Ivy

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/**
 * 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.algo;

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

import org.apache.commons.lang.mutable.MutableInt;

import com.datatorrent.api.DefaultOutputPort;
import com.datatorrent.api.annotation.OperatorAnnotation;

import com.datatorrent.lib.util.AbstractBaseNOperatorMap;

/**
 * This operator filters the incoming stream of key value pairs by emitting the first N key value pairs with a specified key in each window.
 * 
 * Emits first N tuples of a particular key.
 * 
 * 
 * This module is a pass through module

 * 

 * StateFull : Yes,  tuple are compare across application window(s). 

 * Partitions : No,  will yield wrong results. 

 * 

 * Ports:

 * data: Input data port expects HashMap<K,V>

 * bottom: Output data port, emits HashMap<K,V>

 * 

 * Properties:

 * N: The number of top values to be emitted per key

 * 

 * Specific compile time checks are:

 * N: Has to be >= 1

 * 

 * 

 * 
 *
 * @displayName First N Keyval Pairs Matching Key
 * @category Rules and Alerts
 * @tags filter, key value
 *
 * @since 0.3.2
 */
@OperatorAnnotation(partitionable = false)
public class FirstN extends AbstractBaseNOperatorMap
{
  /**
   * key count map.
   */
  HashMap keycount = new HashMap();

  /**
   * Inserts tuples into the queue
   * @param tuple to insert in the queue
   */
  @Override
  public void processTuple(Map tuple)
  {
    for (Map.Entry e: tuple.entrySet()) {
      MutableInt count = keycount.get(e.getKey());
      if (count == null) {
        count = new MutableInt(0);
        keycount.put(e.getKey(), count);
      }
      count.increment();
      if (count.intValue() <= getN()) {
        first.emit(cloneTuple(e.getKey(), e.getValue()));
      }
    }
  }

  /**
   * The output port on which the first N key value pairs are emitted.
   */
  public final transient DefaultOutputPort> first = new DefaultOutputPort>();

  /**
   * Clears the cache to start anew in a new window
   */
  @Override
  public void endWindow()
  {
    keycount.clear();
  }

  /**
   * First N number of KeyValue pairs for each Key.
   *
   * @param val
   */
  public void setN(int val)
  {
    super.setN(val);
  }
}