/**
 * Copyright (C) 2016 LibRec
 * <p>
 * This file is part of LibRec.
 * LibRec is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 * <p>
 * LibRec is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 * <p>
 * You should have received a copy of the GNU General Public License
 * along with LibRec. If not, see <http://www.gnu.org/licenses/>.
 */
package net.librec.similarity;

import java.util.List;

/**
 * Dice Coefficient Similarity
 *
 * @author zhanghaidong
 */
public class DiceCoefficientSimilarity extends AbstractRecommenderSimilarity {

    /**
     * Calculate the similarity between thisList and thatList.
     *
     * @param thisList
     *            this list
     * @param thatList
     *            that list
     * @return similarity
     */
    protected double getSimilarity(List<? extends Number> thisList, List<? extends Number> thatList) {

        double innerProduct = 0.0, thisPower2 = 0.0, thatPower2 = 0.0;
        for (int i = 0; i < thisList.size(); i++) {
            double thisValue = thisList.get(i).doubleValue();
            double thatValue = thatList.get(i).doubleValue();

            innerProduct += thisValue * thatValue;
            thisPower2 += thisValue * thisValue;
            thatPower2 += thatValue * thatValue;
        }

        return 2 * innerProduct / (thisPower2 + thatPower2);
    }
}
