Java计算中位数、方差、标准差、众数

计算中位数：

public static double calculateMedian(double[] values) {
    Arrays.sort(values);
    int middle = values.length / 2;
    if (values.length % 2 == 0) {
        double left = values[middle - 1];
        double right = values[middle];
        return (left + right) / 2;
    } else {
        return values[middle];
    }
}

计算方差和标准差：

public static double calculateVariance(double[] values) {
    double mean = calculateMean(values);
    double sum = 0;
    for (double value : values) {
        sum += Math.pow(value - mean, 2);
    }
    return sum / (values.length - 1);
}

public static double calculateStandardDeviation(double[] values) {
    return Math.sqrt(calculateVariance(values));
}

private static double calculateMean(double[] values) {
    double sum = 0;
    for (double value : values) {
        sum += value;
    }
    return sum / values.length;
}

计算众数：

public static double calculateMode(double[] values) {
    int maxCount = 0;
    double mode = Double.NaN;
    Map<Double, Integer> valueCount = new HashMap<>();
    for (double value : values) {
        int count = valueCount.getOrDefault(value, 0) + 1;
        valueCount.put(value, count);
        if (count > maxCount) {
            maxCount = count;
            mode = value;
        }
    }
    return mode;
}

注意，这里的众数可能不止一个，如果有多个众数，这里只会返回其中一个。