org.conqat.lib.commons.math.StdDevAggregator Maven / Gradle / Ivy
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Provides common utility functions
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/*
* Copyright (c) CQSE GmbH
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.conqat.lib.commons.math;
import java.util.Collection;
/**
* Calculates the standard deviation. This calculation is based on {@link VarianceAggregator}.
*/
public class StdDevAggregator implements IAggregator {
/** The variance aggregator used to calculate the standard deviation. */
private final VarianceAggregator varianceAggregator;
/**
* Constructor.
*
* @param sample
* if true sample standard deviation is calculated, population standard deviation
* otherwise.
*/
public StdDevAggregator(boolean sample) {
varianceAggregator = new VarianceAggregator(sample);
}
/**
* Aggregates by finding the average value
*
* @return {@link Double#NaN} for empty input collection
*/
@Override
public double aggregate(Collection values) {
if (values.isEmpty()) {
return Double.NaN;
}
double variance = varianceAggregator.aggregate(values);
return Math.sqrt(variance);
}
/** Returns {@link Double#NaN}. */
@Override
public double getNeutralElement() {
return Double.NaN;
}
}