001/**
002 * Copyright (c) 2012, 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.ml.sketch.countmin;
031
032import gnu.trove.map.hash.TIntIntHashMap;
033
034import org.openimaj.ml.sketch.SummarySketcher;
035import org.openimaj.util.hash.StringMurmurHashFunction;
036import org.openimaj.util.hash.StringMurmurHashFunctionFactory;
037import org.openimaj.util.pair.IndependentPair;
038
039/**
040 * CountMin as described in the reference below
041 * 
042 * @author Sina Samangooei (ss@ecs.soton.ac.uk)
043 * 
044 */
045public class CountMin implements SummarySketcher<String, Integer> {
046
047        private static class FunctionHashPair extends IndependentPair<StringMurmurHashFunction, TIntIntHashMap> {
048
049                public FunctionHashPair(StringMurmurHashFunction func, TIntIntHashMap map) {
050                        super(func, map);
051
052                }
053        }
054
055        private FunctionHashPair[] maps;
056        private int nwords;
057
058        /**
059         * @param ntables
060         *            the number of hash functions
061         * @param nwords
062         *            the range of the hash functions
063         */
064        public CountMin(int ntables, int nwords) {
065                maps = new FunctionHashPair[ntables];
066                this.nwords = nwords;
067
068                final StringMurmurHashFunctionFactory fact = new StringMurmurHashFunctionFactory();
069                for (int i = 0; i < maps.length; i++) {
070                        maps[i] = new FunctionHashPair(fact.create(), new TIntIntHashMap());
071                }
072        }
073
074        @Override
075        public void update(String data, Integer value) {
076                for (final FunctionHashPair map : this.maps) {
077                        final int hash = map.firstObject().computeHashCode(data);
078                        final int loc = Math.abs(hash) % this.nwords;
079
080                        map.secondObject().adjustOrPutValue(loc, value, value);
081                }
082        }
083
084        @Override
085        public Integer query(String data) {
086                int min = -1;
087                for (final FunctionHashPair map : this.maps) {
088                        final int hash = map.firstObject().computeHashCode(data);
089                        final int loc = Math.abs(hash) % this.nwords;
090                        final int v = map.secondObject().get(loc);
091                        if (min == -1 || min > v) {
092                                min = v;
093                        }
094                }
095                return min;
096        }
097
098}