001    /*--------------------------------------------------------------------------+
002    $Id: MeanAggregator.java 29788 2010-08-19 08:46:02Z juergens $
003    |                                                                          |
004    | Copyright 2005-2010 Technische Universitaet Muenchen                     |
005    |                                                                          |
006    | Licensed under the Apache License, Version 2.0 (the "License");          |
007    | you may not use this file except in compliance with the License.         |
008    | You may obtain a copy of the License at                                  |
009    |                                                                          |
010    |    http://www.apache.org/licenses/LICENSE-2.0                            |
011    |                                                                          |
012    | Unless required by applicable law or agreed to in writing, software      |
013    | distributed under the License is distributed on an "AS IS" BASIS,        |
014    | WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
015    | See the License for the specific language governing permissions and      |
016    | limitations under the License.                                           |
017    +--------------------------------------------------------------------------*/
018    package edu.tum.cs.commons.math;
019    
020    import java.util.Collection;
021    
022    /**
023     * Average aggregator.
024     * 
025     * @author deissenb
026     * @author $Author: juergens $
027     * @version $Rev: 29788 $
028     * @levd.rating GREEN Hash: D9F275FB1C3A1E1F36A477AFCB8F75A2
029     */
030    public class MeanAggregator implements IAggregator {
031    
032            /**
033             * Aggregates by finding the average value
034             * 
035             * @return {@link Double#NaN} for empty input collection
036             */
037            @Override
038            public double aggregate(Collection<? extends Number> values) {
039                    if (values.isEmpty()) {
040                            return Double.NaN;
041                    }
042                    return MathUtils.sum(values) / values.size();
043            }
044    
045            /** Returns {@link Double#NaN}. */
046            @Override
047            public double getNeutralElement() {
048                    return Double.NaN;
049            }
050    }