modules/ml/src/main/java/org/apache/ignite/ml/genetic/RouletteWheelSelectionJob.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.ignite.ml.genetic;

import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Random;
import java.util.stream.Collectors;
import org.apache.ignite.Ignite;
import org.apache.ignite.IgniteCache;
import org.apache.ignite.IgniteException;
import org.apache.ignite.IgniteLogger;
import org.apache.ignite.compute.ComputeJobAdapter;
import org.apache.ignite.ml.genetic.parameter.GAGridConstants;
import org.apache.ignite.resources.IgniteInstanceResource;
import org.apache.ignite.resources.LoggerResource;

/**
 * Responsible for performing Roulette Wheel selection
 */
public class RouletteWheelSelectionJob extends ComputeJobAdapter {
    /** Ignite instance */
    @IgniteInstanceResource
    private Ignite ignite;

    /** Ignite logger */
    @LoggerResource
    private IgniteLogger log;

    /** Total Fitness score */
    Double totalFitnessScore;

    /** Chromosome key/fitness score pair */
    LinkedHashMap<Long, Double> map;

    /**
     * @param totalFitnessScore Total fitness score
     * @param map Chromosome key / fitness score map
     */
    public RouletteWheelSelectionJob(Double totalFitnessScore, LinkedHashMap<Long, Double> map) {
        this.totalFitnessScore = totalFitnessScore;
        this.map = map;
    }

    /**
     * Perform Roulette Wheel selection
     *
     * @return Chromosome parent chosen after 'spinning' the wheel.
     */
    @Override public Chromosome execute() throws IgniteException {

        IgniteCache<Long, Chromosome> populationCache = ignite.cache(GAGridConstants.POPULATION_CACHE);

        int value = spintheWheel(this.totalFitnessScore);

        double partialSum = 0;
        boolean notFound = true;

        //sort map in ascending order by fitness score
        Map<Long, Double> sortedAscendingMap = map.entrySet().stream()
            .sorted(Map.Entry.comparingByValue())
            .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue, (e1, e2) -> e1, LinkedHashMap::new));

        Iterator<Entry<Long, Double>> entries = sortedAscendingMap.entrySet().iterator();

        Long chromosomeKey = (long)-1;

        while (entries.hasNext() && notFound) {
            Entry<Long, Double> entry = entries.next();
            Long key = entry.getKey();
            Double fitnessScore = entry.getValue();
            partialSum += fitnessScore;

            if (partialSum >= value) {
                notFound = false;
                chromosomeKey = key;
            }
        }

        return populationCache.get(chromosomeKey);
    }

    /**
     * Spin the wheel.
     *
     * @param fitnessScore Size of Gene pool
     * @return value
     */
    private int spintheWheel(Double fitnessScore) {
        Random randomGenerator = new Random();
        return randomGenerator.nextInt(fitnessScore.intValue());
    }

}