001/**
002 * Copyright (c) 2011, The University of Southampton and the individual contributors.
003 * All rights reserved.
004 *
005 * Redistribution and use in source and binary forms, with or without modification,
006 * are permitted provided that the following conditions are met:
007 *
008 *   *  Redistributions of source code must retain the above copyright notice,
009 *      this list of conditions and the following disclaimer.
010 *
011 *   *  Redistributions in binary form must reproduce the above copyright notice,
012 *      this list of conditions and the following disclaimer in the documentation
013 *      and/or other materials provided with the distribution.
014 *
015 *   *  Neither the name of the University of Southampton nor the names of its
016 *      contributors may be used to endorse or promote products derived from this
017 *      software without specific prior written permission.
018 *
019 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
020 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
021 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
022 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
023 * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
024 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
025 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
026 * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
027 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
028 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
029 */
030package org.openimaj.experiment.evaluation.retrieval.analysers;
031
032import java.util.List;
033import java.util.Map;
034import java.util.Set;
035
036import org.openimaj.data.identity.Identifiable;
037import org.openimaj.experiment.evaluation.retrieval.RetrievalAnalyser;
038
039/**
040 * {@link RetrievalAnalyser} that computes the precision after N documents have
041 * been retrieved (P@N).
042 * 
043 * @author Jonathon Hare (jsh2@ecs.soton.ac.uk)
044 * 
045 * @param <QUERY>
046 *            Type of query
047 * @param <DOCUMENT>
048 *            Type of document
049 */
050public class PrecisionAtN<QUERY, DOCUMENT extends Identifiable>
051                implements
052                RetrievalAnalyser<PrecisionAtNResult<QUERY>, QUERY, DOCUMENT>
053{
054        protected int N;
055
056        /**
057         * Construct with the given N.
058         * 
059         * @param n
060         *            N, the number of top-ranked documents to consider.
061         */
062        public PrecisionAtN(int n) {
063                N = n;
064        }
065
066        @Override
067        public PrecisionAtNResult<QUERY> analyse(Map<QUERY, List<DOCUMENT>> results, Map<QUERY, Set<DOCUMENT>> relevant) {
068                final PrecisionAtNResult<QUERY> scores = new PrecisionAtNResult<QUERY>(N);
069
070                for (final QUERY query : relevant.keySet()) {
071                        final List<DOCUMENT> qres = results.get(query);
072
073                        if (qres != null) {
074                                final List<DOCUMENT> topN = qres.subList(0, Math.min(N, qres.size()));
075                                scores.allScores.put(query, score(topN, relevant.get(query)));
076                        } else {
077                                scores.allScores.put(query, 0);
078                        }
079                }
080
081                return null;
082        }
083
084        private double score(List<DOCUMENT> topN, Set<DOCUMENT> rel) {
085                int count = 0;
086
087                for (final DOCUMENT ret : topN) {
088                        if (rel.contains(ret))
089                                count++;
090                }
091
092                return (double) count / (double) topN.size();
093        }
094}