library/src/main/java/org/apache/apex/malhar/lib/algo/BottomNUniqueMap.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 org.apache.apex.malhar.lib.algo;

import java.util.ArrayList;
import java.util.HashMap;

import org.apache.apex.malhar.lib.util.AbstractBaseNUniqueOperatorMap;

import com.datatorrent.api.DefaultOutputPort;

/**
 * This operator takes an input stream of key value pairs,
 * orders them by key, and the bottom N of the ordered unique tuples per key are emitted on port "bottom" at the end of window.
 * <p>
 * Input stream of key value pairs are ordered by key, and bottom N of the ordered unique tuples per key are emitted on
 * port "bottom" at the end of window
 * </p>
 * <p>
 * This is an end of window module<br>
 * <br>
 * <b>Ports</b>:<br>
 * <b>data</b>: expects Map&lt;K,V&gt;<br>
 * <b>bottom</b>: emits HashMap&lt;K, ArrayList&lt;HashMap&lt;V,Integer&gt;&gt;&gt;<br>
 * <br>
 * <b>Properties</b>:<br>
 * <b>N</b>: The number of top values to be emitted per key<br>
 * <br>
 * <b>Specific compile time checks are</b>:<br>
 * N: Has to be >= 1<br>
 * </p>
 *
 * @displayName Bottom N Unique Map
 * @category Stats and Aggregations
 * @tags filter, rank, unique, key value
 *
 * @since 0.3.3
 */
public class BottomNUniqueMap<K, V> extends AbstractBaseNUniqueOperatorMap<K, V>
{
  /**
   * The output port on which the unique bottom n tuples per key are emitted.
   */
  public final transient DefaultOutputPort<HashMap<K, ArrayList<HashMap<V,Integer>>>> bottom = new DefaultOutputPort<HashMap<K, ArrayList<HashMap<V,Integer>>>>();

  /**
   * Ascending is set to false as we are looking for Bottom N
   * @return false
   */
  @Override
  public boolean isAscending()
  {
    return false;
  }

  /**
   * Emits tuple to port "bottom"
   * @param tuple
   */
  @Override
  public void emit(HashMap<K, ArrayList<HashMap<V,Integer>>> tuple)
  {
    bottom.emit(tuple);
  }

  /**
   * Bottom N unique tuples.
   * @param val Bottom N unique tuples.
   */
  @Override
  public void setN(int val)
  {
    super.setN(val);
  }
}