[英]Possible to calculate a double sum in python using list comprehensions to replace both for-loops?
[英]Calculate variance of an array using for-loops, Python
我刚刚开始学习 Python,现在我必须使用 for 循环计算数组中的均值和方差。
目前,我得到一个不正确的方差值,我不知道为什么。
numbers = [7, 16, 0.3, 0, 15, -4, 5, 3, 15]
sum = 0
for value in range(0, len(numbers)):
sum = sum + numbers[value]
mean_value = sum / len(numbers)
print(mean_value)
n = len(numbers)
sum_squares = 0
for value in range(0, len(numbers)):
sum_squares = sum_squares + (value - mean_value) ** 2
var_value = sum_squares / n
print(var_value)
根据在线计算器,我应该得到方差 = 55.035,我得到的方差为 12.267
我将不胜感激任何帮助。
ķ
编辑:我刚刚意识到将第二部分更改为此有效:
for value in numbers:
sum_squares = sum_squares + ((value - mean_value) ** 2)
var_value = sum_squares / n
不确定“for value in numbers:”和“for value in range(0, len(numbers)):”之间的确切区别是什么,但这是有帮助的。
方差除以 (n-1)
numbers = [7, 16, 0.3, 0, 15, -4, 5, 3, 15]
sum = 0
count = 0
sum_squares = 0
for value in numbers:
sum = sum + value
count = count + 1
mean_value = (sum / count)
for value in numbers:
sum_squares = sum_squares + ((value - mean_value)** 2)
var_value = sum_squares / (count-1)
print (mean_value)
print (var_value)
出去:
6.366666666666666
55.035
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