Precision.java

/* 
 * Copyright (C) 2015 Information Retrieval Group at Universidad Autónoma
 * de Madrid, http://ir.ii.uam.es
 *
 * 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 es.uam.eps.ir.ranksys.metrics.basic;

import es.uam.eps.ir.ranksys.metrics.rel.RelevanceModel;
import es.uam.eps.ir.ranksys.core.Recommendation;
import es.uam.eps.ir.ranksys.metrics.AbstractRecommendationMetric;
import es.uam.eps.ir.ranksys.metrics.rel.RelevanceModel.UserRelevanceModel;
import org.ranksys.core.util.tuples.Tuple2od;

/**
 * Precision metric: proportion of relevant items in a recommendation list.
 *
 * @author Saúl Vargas (saul.vargas@uam.es)
 * @author Pablo Castells (pablo.castells@uam.es)
 * 
 * @param <U> type of the users
 * @param <I> type of the items
 */
public class Precision<U, I> extends AbstractRecommendationMetric<U, I> {

    private final RelevanceModel<U, I> relModel;
    private final int cutoff;

    /**
     * Constructor.
     *
     * @param cutoff maximum length of recommended lists
     * @param relModel relevance model
     */
    public Precision(int cutoff, RelevanceModel<U, I> relModel) {
        this.relModel = relModel;
        this.cutoff = cutoff;
    }

    /**
     * Returns a score for the recommendation list.
     *
     * @param recommendation recommendation list
     * @return score of the metric to the recommendation
     */
    @Override
    public double evaluate(Recommendation<U, I> recommendation) {
        UserRelevanceModel<U, I> userRelModel = relModel.getModel(recommendation.getUser());
        
        return recommendation.getItems().stream()
                .limit(cutoff)
                .map(Tuple2od::v1)
                .filter(userRelModel::isRelevant)
                .count() / (double) cutoff;
    }
}