source: sample/hadoop-0.17/tw/org/nchc/util/InstanceCounter.java

/*
 * Cloud9: A MapReduce Library for Hadoop
 * 
 * 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 tw.org.nchc.util;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Map;
import java.util.SortedSet;
import java.util.TreeSet;

/**
 * A class for keeping track of the number of times an object has been
 * encountered. This is useful for counting things in a stream, e.g., POS tags,
 * terms, etc.
 */
public class InstanceCounter<T extends Comparable<T>> {

  // internal representation---although the scores are doubles, counts are
  // obviously integers
  private ScoreSortedMap<T> mMap;

  private int mTotalCount = 0;

  /**
   * Constructs an <code>InstanceCounter</code>.
   */
  public InstanceCounter() {
    mMap = new ScoreSortedMap<T>();
  }

  /**
   * Adds an instance to the set of observations.
   * 
   * @param instance
   *            the instance observed
   */
  public void count(T instance) {
    if (mMap.containsKey(instance)) {
      mMap.put(instance, mMap.get(instance) + 1);
    } else {
      mMap.put(instance, 1.0);
    }
    mTotalCount++;
  }

  /**
   * Prints each instance and how many times its been observed, sorted by the
   * counts.
   */
  public void printCounts() {
    for (Map.Entry<T, Double> map : mMap.getSortedEntries()) {
      System.out.println(map.getValue().intValue() + "\t" + map.getKey());
    }
  }

  /**
   * Returns a list of <code>InstanceCount</code> objects, sorted by count.
   */
  public List<InstanceCount> getCounts() {
    List<InstanceCount> l = new ArrayList<InstanceCount>();

    for (Map.Entry<T, Double> map : mMap.getSortedEntries()) {
      l.add(new InstanceCount(map.getKey(), map.getValue().intValue(),
          map.getValue() / (double) mTotalCount));
    }

    return Collections.unmodifiableList(l);
  }

  /**
   * Returns the total number of observations.
   * 
   * @return the total number of observations
   */
  public int getTotalCount() {
    return mTotalCount;
  }

  /**
   * Returns the number of times a particular instance has been observed.
   * 
   * @param inst
   *            the instance
   * @return the count of the instance
   */
  public int getCount(T inst) {
    if (mMap.containsKey(inst)) {
      return mMap.get(inst).intValue();
    }

    return 0;
  }

  /**
   * Returns a collection of all objects observed, sorted by their natural
   * order.
   * 
   * @return a collection of all objects observed, sorted by their natural
   *         order.
   */
  public SortedSet<T> getObservedObjects() {
    SortedSet<T> t = new TreeSet<T>();

    for (T obj : mMap.keySet()) {
      t.add(obj);
    }

    return t;
  }

  /**
   * A class that holds an instance, its count, and its frequency.
   */
  public class InstanceCount {
    private T mInstance;

    private int mCount;

    private double mFreq;

    private InstanceCount(T instance, int cnt, double freq) {
      mInstance = instance;
      mCount = cnt;
      mFreq = freq;
    }

    /**
     * Returns the instance.
     */
    public T getInstance() {
      return mInstance;
    }

    /**
     * Returns the number of times the instance has been observed.
     */
    public int getCount() {
      return mCount;
    }

    /**
     * Returns the frequency that this instance has been observed. Frequency
     * is the count divided by the total number of observed instances.
     */
    public double getFrequency() {
      return mFreq;
    }
  }

  public void clear() {
    mMap.clear();
  }

}