examples/src/main/java/org/apache/ignite/examples/ml/genetic/movie/MovieFitnessFunction.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.examples.ml.genetic.movie;

import java.util.ArrayList;
import java.util.List;
import org.apache.ignite.ml.genetic.Gene;
import org.apache.ignite.ml.genetic.IFitnessFunction;

/**
 * This example demonstrates how to create a {@link IFitnessFunction}.
 * <p>
 * Your fitness function will vary depending on your particular use case. For this fitness function, we want to
 * calculate the value of an individual solution relative to other solutions.</p>
 * <p>
 * To do this, we increase fitness score by number of times genre is found in list of movies. In addition, we increase
 * score by fictional IMDB rating.</p>
 * <p>
 * If there are duplicate movies in selection, we automatically apply a '0' fitness score.</p>
 */
public class MovieFitnessFunction implements IFitnessFunction {
    /**
     * Genres.
     */
    private List<String> genres;

    /**
     * Create instance.
     *
     * @param genres List of genres.
     */
    public MovieFitnessFunction(List<String> genres) {
        this.genres = genres;
    }

    /**
     * {@inheritDoc}
     */
    @Override public double evaluate(List<Gene> genes) {
        double score = 0;
        List<String> duplicates = new ArrayList<>();
        int badSolution = 1;

        for (Gene gene : genes) {
            Movie movie = (Movie)gene.getVal();
            if (duplicates.contains(movie.getName()))
                badSolution = 0;
            else
                duplicates.add(movie.getName());

            double genreScore = getGenreScore(movie);
            if (genreScore == 0)
                badSolution = 0;

            score = (score + movie.getImdbRating()) + (genreScore);
        }
        return (score * badSolution);
    }

    /**
     * Helper to calculate genre score.
     *
     * @param movie Movie.
     * @return Genre score.
     */
    private double getGenreScore(Movie movie) {
        double genreScore = 0;

        for (String genre : genres) {
            if (movie.getGenre().contains(genre))
                genreScore += 1;
        }
        return genreScore;
    }
}