Stats.java

/*
 * Copyright (C) 2019, Matthias Sohn <matthias.sohn@sap.com> and others
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Distribution License v. 1.0 which is available at
 * https://www.eclipse.org/org/documents/edl-v10.php.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */
package org.eclipse.jgit.util;

/**
 * Simple double statistics, computed incrementally, variance and standard
 * deviation using Welford's online algorithm, see
 * https://en.wikipedia.org/wiki/Algorithms_for_calculating_variance#Welford's_online_algorithm
 *
 * @since 5.1.9
 */
public class Stats {
    private int n = 0;

    private double avg = 0.0;

    private double min = 0.0;

    private double max = 0.0;

    private double sum = 0.0;

    /**
     * Add a value
     *
     * @param x
     *            value
     */
    public void add(double x) {
        n++;
        min = n == 1 ? x : Math.min(min, x);
        max = n == 1 ? x : Math.max(max, x);
        double d = x - avg;
        avg += d / n;
        sum += d * d * (n - 1) / n;
    }

    /**
     * @return number of the added values
     */
    public int count() {
        return n;
    }

    /**
     * @return minimum of the added values
     */
    public double min() {
        if (n < 1) {
            return Double.NaN;
        }
        return min;
    }

    /**
     * @return maximum of the added values
     */
    public double max() {
        if (n < 1) {
            return Double.NaN;
        }
        return max;
    }

    /**
     * @return average of the added values
     */

    public double avg() {
        if (n < 1) {
            return Double.NaN;
        }
        return avg;
    }

    /**
     * @return variance of the added values
     */
    public double var() {
        if (n < 2) {
            return Double.NaN;
        }
        return sum / (n - 1);
    }

    /**
     * @return standard deviation of the added values
     */
    public double stddev() {
        return Math.sqrt(this.var());
    }
}