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.stream.window;
031
032import java.util.HashMap;
033import java.util.List;
034import java.util.Map;
035import java.util.Map.Entry;
036
037import org.openimaj.util.function.Function;
038
039/**
040 * Given a window of key,value map instances, this function gets the average of
041 * the window
042 * 
043 * @author Sina Samangooei (ss@ecs.soton.ac.uk)
044 * 
045 */
046public class WindowAverage implements Function<List<Map<String, Double>>, Map<String, Double>> {
047
048        @Override
049        public Map<String, Double> apply(List<Map<String, Double>> in) {
050
051                final Map<String, Double> ret = new HashMap<String, Double>();
052                final Map<String, Long> count = new HashMap<String, Long>();
053
054                for (final Map<String, Double> map : in) {
055                        for (final Entry<String, Double> item : map.entrySet()) {
056                                final String key = item.getKey();
057                                if (!count.containsKey(key)) {
058                                        ret.put(key, item.getValue());
059                                        count.put(key, 1l);
060                                }
061                                else {
062                                        ret.put(key, ret.get(key) + item.getValue());
063                                        count.put(key, count.get(key) + 1);
064                                }
065                        }
066                }
067                for (final Entry<String, Double> map : ret.entrySet()) {
068                        final String key = map.getKey();
069                        ret.put(key, map.getValue() / count.get(key));
070                }
071                return ret;
072        }
073
074}