Java tutorial
/* * 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.kylin.cube.cuboid.algorithm.generic; import com.google.common.collect.Lists; import org.apache.commons.math3.genetics.Chromosome; import org.apache.commons.math3.genetics.ChromosomePair; import org.apache.commons.math3.genetics.GeneticAlgorithm; import org.apache.commons.math3.genetics.ListPopulation; import org.apache.commons.math3.genetics.Population; import org.apache.commons.math3.genetics.SelectionPolicy; import java.util.List; public class RouletteWheelSelection implements SelectionPolicy { @Override public ChromosomePair select(Population population) throws IllegalArgumentException { // create a copy of the chromosome list List<Chromosome> chromosomes = Lists.newArrayList(((ListPopulation) population).getChromosomes()); double maxFitness = 0; double totalFitness = 0; for (Chromosome o : chromosomes) { double fitness = o.getFitness(); totalFitness += fitness; if (fitness > maxFitness) { maxFitness = fitness; } } return new ChromosomePair(rouletteWheel(chromosomes, totalFitness), rouletteWheel(chromosomes, totalFitness)); } private Chromosome rouletteWheel(final List<Chromosome> chromosomes, final double totalFitness) { double rnd = (GeneticAlgorithm.getRandomGenerator().nextDouble() * totalFitness); double runningScore = 0; for (Chromosome o : chromosomes) { if (rnd >= runningScore && rnd <= runningScore + o.getFitness()) { return o; } runningScore += o.getFitness(); } return null; } }