001/*-------------------------------------------------------------------------+
002|                                                                          |
003| Copyright 2005-2011 The ConQAT Project                                   |
004|                                                                          |
005| Licensed under the Apache License, Version 2.0 (the "License");          |
006| you may not use this file except in compliance with the License.         |
007| You may obtain a copy of the License at                                  |
008|                                                                          |
009|    http://www.apache.org/licenses/LICENSE-2.0                            |
010|                                                                          |
011| Unless required by applicable law or agreed to in writing, software      |
012| distributed under the License is distributed on an "AS IS" BASIS,        |
013| WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
014| See the License for the specific language governing permissions and      |
015| limitations under the License.                                           |
016+-------------------------------------------------------------------------*/
017package org.conqat.lib.commons.math;
018
019import java.util.Collection;
020
021/**
022 * Average aggregator.
023 * 
024 * @author deissenb
025 */
026public class MeanAggregator implements IAggregator {
027
028        /**
029         * Aggregates by finding the average value
030         * 
031         * @return {@link Double#NaN} for empty input collection
032         */
033        @Override
034        public double aggregate(Collection<? extends Number> values) {
035                if (values.isEmpty()) {
036                        return Double.NaN;
037                }
038                return MathUtils.sum(values) / values.size();
039        }
040
041        /** Returns {@link Double#NaN}. */
042        @Override
043        public double getNeutralElement() {
044                return Double.NaN;
045        }
046}