如何解决在Python中计算均值和方差
当您输入一组数字时,我有这段代码可以计算均值和方差,但是我的方差与实际值不符。是我的方差公式不正确还是在我的代码中可能有错误?
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 0.5
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 ',variance)
解决方法
您的方差公式是错误的。您可以找到here的公式以更好地理解,这里我不做解释。
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 ',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
您输入了错误的测试用例,
Input a positive number: 3
mean is 2.0 variance is 0.1
在这里,差异将为1 not 0.1
。您可以使用online calculator.
您可以使用列表存储所有输入。
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 "," variance is ",var)
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