001package org.cpsolver.ifs.heuristics;
002
003import java.util.ArrayList;
004import java.util.Enumeration;
005import java.util.List;
006
007import org.cpsolver.ifs.util.ToolBox;
008
009
010/**
011 * A general roulette wheel selection. An object is selected randomly,
012 * proportionaly to the provided weight. This class also supports multiple
013 * selections (it implements {@link Enumeration} interface).
014 * 
015 * <br>
016 * <br>
017 * 
018 * @version StudentSct 1.3 (Student Sectioning)<br>
019 *          Copyright (C) 2007 - 2014 Tomas Muller<br>
020 *          <a href="mailto:muller@unitime.org">muller@unitime.org</a><br>
021 *          <a href="http://muller.unitime.org">http://muller.unitime.org</a><br>
022 * <br>
023 *          This library is free software; you can redistribute it and/or modify
024 *          it under the terms of the GNU Lesser General Public License as
025 *          published by the Free Software Foundation; either version 3 of the
026 *          License, or (at your option) any later version. <br>
027 * <br>
028 *          This library is distributed in the hope that it will be useful, but
029 *          WITHOUT ANY WARRANTY; without even the implied warranty of
030 *          MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
031 *          Lesser General Public License for more details. <br>
032 * <br>
033 *          You should have received a copy of the GNU Lesser General Public
034 *          License along with this library; if not see
035 *          <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
036 * 
037 * @param <E> Class of objects that are to be selected from. 
038 */
039public class RouletteWheelSelection<E> implements Enumeration<E> {
040    private List<E> iAdepts = new ArrayList<E>();
041    private List<Double> iPoints = new ArrayList<Double>();
042    private double iTotalPoints = 0, iUsedPoints = 0;
043    private int iFirst = 0;
044
045    /**
046     * Add an adept to the selection
047     * 
048     * @param adept
049     *            an object
050     * @param points
051     *            object weight (more points, better chance to be selected)
052     */
053    public void add(E adept, double points) {
054        iAdepts.add(adept);
055        iPoints.add(points);
056        iTotalPoints += points;
057    }
058
059    private void swap(int idx1, int idx2) {
060        E a1 = iAdepts.get(idx1);
061        E a2 = iAdepts.get(idx2);
062        iAdepts.set(idx1, a2);
063        iAdepts.set(idx2, a1);
064        Double p1 = iPoints.get(idx1);
065        Double p2 = iPoints.get(idx2);
066        iPoints.set(idx1, p2);
067        iPoints.set(idx2, p1);
068    }
069
070    /** Are there still some adepts that have not been yet selected */
071    @Override
072    public boolean hasMoreElements() {
073        return iFirst < iAdepts.size();
074    }
075
076    /**
077     * Perform selection. An object is selected randomly with the probability
078     * proportional to the provided weight. Each object can be selected only
079     * once.
080     */
081    @Override
082    public E nextElement() {
083        if (!hasMoreElements())
084            return null;
085        double rx = ToolBox.random() * iTotalPoints;
086
087        int iIdx = iFirst;
088        rx -= iPoints.get(iIdx);
089        while (rx > 0 && iIdx + 1 < iAdepts.size()) {
090            iIdx++;
091            rx -= iPoints.get(iIdx);
092        }
093
094        E selectedObject = iAdepts.get(iIdx);
095        double points = iPoints.get(iIdx);
096        iTotalPoints -= points;
097        iUsedPoints += points;
098        swap(iFirst, iIdx);
099        iFirst++;
100
101        return selectedObject;
102    }
103
104    /** Number of objects in the set 
105     * @return number of objects in the set
106     **/
107    public int size() {
108        return iAdepts.size();
109    }
110
111    /** Total value of objects that were already returned by the selection.
112     * @return total value of objects that were already returned by the selection
113     **/
114    public double getUsedPoints() {
115        return iUsedPoints;
116    }
117
118    /** Total value of objects that are still in the selection.
119     * @return total value of objects that are still in the selection
120     **/
121    public double getRemainingPoints() {
122        return iTotalPoints;
123    }
124
125    /** Total value of objects that were added into the selection.
126     * @return total value of objects that were added into the selection
127     **/
128    public double getTotalPoints() {
129        return iTotalPoints + iUsedPoints;
130    }
131}