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RankSys module, providing diversity metrics and enhancement techniques.

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/* 
 * Copyright (C) 2015 RankSys (http://ranksys.org)
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 */
package org.ranksys.diversity.prop.reranking;

import es.uam.eps.ir.ranksys.core.feature.FeatureData;
import es.uam.eps.ir.ranksys.core.Recommendation;
import es.uam.eps.ir.ranksys.diversity.binom.BinomialModel;
import es.uam.eps.ir.ranksys.novdiv.reranking.GreedyReranker;
import it.unimi.dsi.fastutil.objects.Object2DoubleOpenHashMap;
import org.jooq.lambda.tuple.Tuple2;
import org.ranksys.core.util.tuples.Tuple2od;

/**
 * Proportionality re-ranking method.
 * 

 * 
 * Dang, V., Croft, W. B. (2012). Diversity by Proportionality: An Election-based Approach to Search Result Diversification. In Proceedings of the 35th International ACM SIGIR Conference on Research and Development in Information Retrieval (pp. 65–74). New York, NY, USA: ACM. doi:10.1145/2348283.2348296
 *
 * @author Saúl Vargas ([email protected])
 *
 * @param  type of user
 * @param  type of item
 * @param  type of feature
 */
public class PM extends GreedyReranker {

    private final double lambda;
    private final FeatureData featureData;
    private final BinomialModel binomialModel;

    /**
     * Constructor.
     *
     * @param binomialModel binomial model for features
     * @param featureData feature data
     * @param lambda relevance-diversity tradeoff
     * @param cutoff metric cutoff
     */
    public PM(FeatureData featureData, BinomialModel binomialModel, double lambda, int cutoff) {
        super(cutoff);
        this.lambda = lambda;
        this.featureData = featureData;
        this.binomialModel = binomialModel;
    }

    @Override
    protected GreedyUserReranker getUserReranker(Recommendation recommendation, int maxLength) {
        return new UserPM(recommendation, maxLength);
    }

    private class UserPM extends GreedyUserReranker {

        private final BinomialModel.UserBinomialModel ubm;
        private final Object2DoubleOpenHashMap featureCount;
        private final Object2DoubleOpenHashMap