library/src/main/java/org/apache/apex/malhar/lib/util/AbstractBaseFrequentKey.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.util;

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

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

/**
 * This is the base implementation of an operator, which counts the number of times each tuple occurs. 
 * The counts of tuples are then compared at the end of each window and the winning tuple(s) are emitted. 
 * Subclasses should implement the methods that are used to emit tuples, as well as the comparison method used
 * to determine the winning tuple(s).
 * <p>
 * This module is an end of window module.
 * </p>
 *
 * @displayName Emit Winning Value(s)
 * @category Algorithmic
 * @tags count, compare
 * @since 0.3.2
 */
public abstract class AbstractBaseFrequentKey<K> extends BaseKeyOperator<K>
{
  /**
   * Counts frequency of a key
   * @param tuple
   */
  public void processTuple(K tuple)
  {
    MutableInt count = keycount.get(tuple);
    if (count == null) {
      count = new MutableInt(0);
      keycount.put(cloneKey(tuple), count);
    }
    count.increment();
  }

  protected HashMap<K, MutableInt> keycount = new HashMap<K, MutableInt>();

  /**
   * override emitTuple to decide the port to emit to
   * @param tuple
   */
  public abstract void emitTuple(HashMap<K,Integer> tuple);

  /**
   * Overide emitList to specify the emit schema
   * @param tlist
   */
  public abstract void emitList(ArrayList<HashMap<K, Integer>> tlist);

  /**
   * Override compareCount to decide most vs least
   * @param val1
   * @param val2
   * @return result of compareCount to be done by subclass
   */
  public abstract boolean compareCount(int val1, int val2);

  /**
   * Emits the result.
   */
  @Override
  public void endWindow()
  {
    // Compute least frequent
    K key = null;
    int kval = -1;
    HashMap<K, Object> map = new HashMap<K, Object>();
    for (Map.Entry<K, MutableInt> e: keycount.entrySet()) {
      if ((kval == -1)) {
        key = e.getKey();
        kval = e.getValue().intValue();
        map.put(key, null);
      } else if (compareCount(e.getValue().intValue(), kval)) {
        key = e.getKey();
        kval = e.getValue().intValue();
        map.clear();
        map.put(key, null);
      } else if (e.getValue().intValue() == kval) {
        map.put(e.getKey(), null);
      }
    }

    // Emit least frequent key, emit all least frequent keys list
    // on other ports.
    HashMap<K, Integer> tuple;
    if ((key != null) && (kval > 0)) {
      tuple = new HashMap<K, Integer>(1);
      tuple.put(key, new Integer(kval));
      emitTuple(tuple);
      ArrayList<HashMap<K, Integer>> elist = new ArrayList<HashMap<K, Integer>>();
      for (Map.Entry<K, Object> e: map.entrySet()) {
        tuple = new HashMap<K, Integer>(1);
        tuple.put(e.getKey(), kval);
        elist.add(tuple);
      }
      emitList(elist);
    }
    keycount.clear();
  }
}