StatisticsUtils.java

public class StatisticsUtils {

    /**
     * Computes the Coefficient of Variation (CV) from an array of doubles.
     * Handles cases where the mean is zero by returning a modified CV using the absolute mean.
     * @param data An array of doubles.
     * @return The Coefficient of Variation (CV).
     */
    public static double computeCV(double[] data) {
        if (data == null || data.length == 0) {
            throw new IllegalArgumentException("Data array is null or empty");
        }

        double mean = computeMean(data);
        double absMean = Math.abs(mean);

        // If mean is zero, return Double.POSITIVE_INFINITY
        if (absMean == 0) {
            return Double.POSITIVE_INFINITY; // Extreme variability
        }

        double stdDev = computeStandardDeviation(data, mean);
        return stdDev / absMean;
    }

    /**
     * Computes a range-based variability measure using standard deviation over the actual data range.
     * @param data An array of doubles.
     * @return The variability relative to the range.
     */
    public static double computeRangeBasedVariability(double[] data) {
        if (data == null || data.length == 0) {
            throw new IllegalArgumentException("Data array is null or empty");
        }

        double min = findMin(data);
        double max = findMax(data);
        double range = max - min;

        if (range == 0) {
            return 0.0; // No variability if all values are the same
        }

        double mean = computeMean(data);
        double stdDev = computeStandardDeviation(data, mean);
        return stdDev / range;
    }

    /**
     * Computes a range-based variability measure using standard deviation over a user-specified range.
     * @param data An array of doubles.
     * @param specifiedMin The minimum value of the range.
     * @param specifiedMax The maximum value of the range.
     * @return The variability relative to the specified range.
     */
    public static double computeRangeBasedVariability(double[] data, double specifiedMin, double specifiedMax) {
        if (data == null || data.length == 0) {
            throw new IllegalArgumentException("Data array is null or empty");
        }

        double range = specifiedMax - specifiedMin;

        if (range <= 0) {
            throw new IllegalArgumentException("Specified range must be greater than zero");
        }

        double mean = computeMean(data);
        double stdDev = computeStandardDeviation(data, mean);
        return stdDev / range;
    }

    /**
     * Helper method to compute the mean for an array.
     */
    private static double computeMean(double[] data) {
        double sum = 0.0;
        for (double num : data) {
            sum += num;
        }
        return sum / data.length;
    }

    /**
     * Helper method to compute the standard deviation for an array.
     */
    private static double computeStandardDeviation(double[] data, double mean) {
        double varianceSum = 0.0;
        for (double num : data) {
            varianceSum += Math.pow(num - mean, 2);
        }
        return Math.sqrt(varianceSum / data.length);
    }

    /**
     * Helper method to find the minimum value in an array.
     */
    private static double findMin(double[] data) {
        double min = Double.MAX_VALUE;
        for (double num : data) {
            if (num < min) {
                min = num;
            }
        }
        return min;
    }

    /**
     * Helper method to find the maximum value in an array.
     */
    private static double findMax(double[] data) {
        double max = -Double.MAX_VALUE;
        for (double num : data) {
            if (num > max) {
                max = num;
            }
        }
        return max;
    }

    public static void main(String[] args) {
        // Example data: temperature readings
        double[] dataArray = {-5.0, -2.5, 0.0, 2.5, 5.0};

        // Compute Coefficient of Variation (CV)
        try {
            double cv = computeCV(dataArray);
            System.out.printf("CV (array): %.4f%n", cv);
        } catch (ArithmeticException | IllegalArgumentException e) {
            System.out.println("Error (CV): " + e.getMessage());
        }

        // Compute range-based variability (actual range)
        try {
            double rangeVar = computeRangeBasedVariability(dataArray);
            System.out.printf("Range-Based Variability (actual range): %.4f%n", rangeVar);
        } catch (IllegalArgumentException e) {
            System.out.println("Error (Range-Based Variability): " + e.getMessage());
        }

        // Compute range-based variability (specified range)
        try {
            double rangeVarSpecified = computeRangeBasedVariability(dataArray, -10.0, 10.0);
            System.out.printf("Range-Based Variability (specified range): %.4f%n", rangeVarSpecified);
        } catch (IllegalArgumentException e) {
            System.out.println("Error (Range-Based Variability with Specified Range): " + e.getMessage());
        }
    }
}