使用java計算數組方差和標准差

覺得有用的話,歡迎一起討論相互學習~

首先給出方差和標准差的計算公式

代碼

public class Cal_sta {
    double Sum(double[] data) {
        double sum = 0;
        for (int i = 0; i < data.length; i++)
            sum = sum + data[i];
        return sum;
    }

    double Mean(double[] data) {
        double mean = 0;
        mean = Sum(data) / data.length;
        return mean;
    }

    // population variance 總體方差
    double POP_Variance(double[] data) {
        double variance = 0;
        for (int i = 0; i < data.length; i++) {
            variance = variance + (Math.pow((data[i] - Mean(data)), 2));
        }
        variance = variance / data.length;
        return variance;
    }

    // population standard deviation 總體標准差
    double POP_STD_dev(double[] data) {
        double std_dev;
        std_dev = Math.sqrt(POP_Variance(data));
        return std_dev;
    }

    //sample variance 樣本方差
    double Sample_Variance(double[] data) {
        double variance = 0;
        for (int i = 0; i < data.length; i++) {
            variance = variance + (Math.pow((data[i] - Mean(data)), 2));
        }
        variance = variance / (data.length-1);
        return variance;
    }

    // sample standard deviation 樣本標准差
    double Sample_STD_dev(double[] data) {
        double std_dev;
        std_dev = Math.sqrt(Sample_Variance(data));
        return std_dev;
    }

}

測試代碼

public class testcal_sta {
    public static void main(String arg[]) {
        Cal_sta cal = new Cal_sta();
        double[] testdata = {2, 4, 6, 7, 8, 9, 12, 36};
        System.out.println("總和Sum  " + cal.Sum(testdata));
        System.out.println("平均值Mean  " + cal.Mean(testdata));
        System.out.println("總體方差Population Variance  " + cal.POP_Variance(testdata));
        System.out.println("總體標准差Population STD_dev   " + cal.POP_STD_dev(testdata));
        System.out.println("樣本方差Sample Variance  " + cal.Sample_Variance(testdata));
        System.out.println("樣本標准差Sample STD_dev   " + cal.Sample_STD_dev(testdata));
    }
}

結果

對比