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.util;
031
032import java.util.ArrayList;
033import java.util.Collection;
034import java.util.List;
035
036import org.openimaj.data.RandomData;
037
038/**
039 * Implementation of a {@link CollectionSampler} that performs uniform sampling.
040 * Each sampled set is sampled without replacement (i.e. an item will only
041 * appear once), however there is no guarantee that subsequent calls to
042 * {@link #sample(int)} will return unique sets of samples.
043 * 
044 * @author Jonathon Hare (jsh2@ecs.soton.ac.uk)
045 * 
046 * @param <T>
047 *            type of items in the collection being sampled
048 */
049public class UniformSampler<T> implements CollectionSampler<T> {
050        private List<T> data;
051
052        @Override
053        public void setCollection(Collection<? extends T> collection) {
054                this.data = new ArrayList<T>(collection);
055        }
056
057        @Override
058        public List<T> sample(int nItems) {
059                final int[] rints = RandomData.getUniqueRandomInts(nItems, 0, data.size());
060                final List<T> out = new ArrayList<T>(nItems);
061
062                for (final int i : rints) {
063                        out.add(data.get(i));
064                }
065
066                return out;
067        }
068}