计算 python 中的均值和方差

Question

我有这段代码可以在您输入一组数字时计算均值和方差，但我的方差与应有的不符。我的方差公式是否以某种方式关闭或者我的代码中可能存在一些错误？

我的输出：

Input a positive number: 1
mean is  1.0 variance is  0

Input a positive number: 2
mean is  1.5 variance is  0.125

Input a positive number: 3
mean is  2.0 variance is  0.3958333333333333

正确输出：

Input a positive number: 1
mean is  1.0 variance is  0

Input a positive number: 2
mean is  1.5 variance is  0.5

Input a positive number: 3
mean is  2.0 variance is  1

mean = 0
variance = 0
x = 0
n = 0
while x >= 0:
    x = float(input('Input a positive number: '))  # user input for code
    n += 1
    if x < 0:
        break

    if n == 1:  # Added this if statement to avoid dividing by 0
        mean = x
        print('mean is ', mean, 'variance is ', variance)
    else:
        mean = mean + ((x-mean)/n)  # formula for calculating mean
        variance = (((n-2)/(n-1)) * variance) + (((mean-x)**2)/n)  # formula for calculating variance
        print('mean is ', mean, 'variance is ', variance)

Answer 1

您可以使用列表来存储所有输入。

x = 0
data = [] 
while x >= 0:
    x = float(input('Input a positive number: '))  # user input for code
    if x < 0:
         break

    data.append(x)        
    N = len(data)
    mean = sum(data) / N

    var = 0
    if N > 1:
        a = [x - mean for x in data]
        a = [x**2 for x in a]
        var = sum( a) / (N-1)
    
    print( "mean is ", mean, " variance is ", var)

Answer 2

你的方差公式是错误的。大家可以找here公式更好理解，这里就不解释了

mean = 0
variance = 0
x = 0
n = 0
while x >= 0:
    x = float(input('Input a positive number: '))  # user input for code
    n += 1
    if x < 0:
        break

    if n == 1:  # Added this if statement to avoid dividing by 0
        mean = x
        print('mean is ', mean, 'variance is ', variance)
    else:
        mean = mean + ((x-mean)/n)  # formula for calculating mean
        
        variance = (((n-2)/(n-1)) * variance) + (((x-mean)*(x-pre_mean))/(n-1))  # formula for calculating variance
        print('mean is ', mean, 'variance is ', variance)
    pre_mean = mean

输出：

Input a positive number: 1
mean is  1.0 variance is  0
Input a positive number: 2
mean is  1.5 variance is  0.5
Input a positive number: 3
mean is  2.0 variance is  1.0
Input a positive number: 4
mean is  2.5 variance is  1.6666666666666665

你给错了测试用例，

Input a positive number: 3
mean is  2.0 variance is  0.1

此处，方差将 1 not 0.1。您可以使用 online calculator.

轻松检查样本方差

计算 python 中的均值和方差

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