Example usage for org.apache.commons.math.stat.descriptive SummaryStatistics getVarianceImpl

Introduction

In this page you can find the example usage for org.apache.commons.math.stat.descriptive SummaryStatistics getVarianceImpl.

Prototype

public StorelessUnivariateStatistic getVarianceImpl() 

Source Link

Document

Returns the currently configured variance implementation

Usage

From source file:uk.ac.diamond.scisoft.analysis.dataset.AbstractDataset.java

/**
 * The sample variance can be calculated in two ways: if the dataset is considered as the entire population then the
 * sample variance is simply the second central moment:
 * //from w w w.  ja  v a  2  s.co m
 * <pre>
 *    sum((x_i - m)^2)/N
 * where {x_i} are set of N population values and m is the mean
 *    m = sum(x_i)/N
 * </pre>
 * 
 * Otherwise, if the dataset is a set of samples (with replacement) from the population then
 * 
 * <pre>
 *    sum((x_i - m)^2)/(N-1)
 * where {x_i} are set of N sample values and m is the unbiased estimate of the mean
 *    m = sum(x_i)/N
 * </pre>
 * 
 * Note that the second definition is also the unbiased estimator of population variance.
 * 
 * @param isDatasetWholePopulation
 * @return sample variance
 */
public Number variance(boolean isDatasetWholePopulation) {
    SummaryStatistics stats = getStatistics();

    if (isDatasetWholePopulation) {
        StorelessUnivariateStatistic oldVar = stats.getVarianceImpl();
        stats.setVarianceImpl(new Variance(false));
        Number var = stats.getVariance();
        stats.setVarianceImpl(oldVar);
        return var;
    }
    return stats.getVariance();
}

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