清单清单的python平均值 [英] python mean of list of lists

问题描述

我想从包含正负数的列表中找到所有负数的均值.我可以找到列表的平均值为

I want to find the means of all the negative numbers from a list that has a mix of positive and negative numbers. I can find the mean of the lists as

import numpy as np

listA = [ [2,3,-7,-4] , [-2,3,4,-5] , [-5,-6,-8,2] , [9,5,13,2]  ]
listofmeans = [np.mean(i) for i in listA ]

我想创建一个类似的单行代码，仅采用列表中负数的均值.因此，例如，新列表的第一个元素是(-7 + -4)/2 = -5.5

I want to create a similar one line code that only takes the mean of the negative numbers in the list. So for example the first element of the new list would be (-7 + -4)/2 = -5.5

我的完整列表是:

listofnegativemeans = [ -5.5, -3.5, -6.333333, 0 ] 

推荐答案

您可以使用以下内容:

listA = [[2,3,-7,-4], [-2,3,4,-5], [-5,-6,-8,2], [9,5,13,2]]
means = [np.mean([el for el in sublist if el < 0] or 0) for sublist in listA]
print(means)

输出

[-5.5, -3.5, -6.3333, 0.0]

如果sublist中的所有元素都不小于0，则列表推导的值将为[].通过包含表达式[] or 0，我们可以处理您要计算空列表的均值为0的情况.

If none of the elements in sublist are less than 0, the list comprehension will evaluate to []. By including the expression [] or 0 we handle your scenario where you want to evaluate the mean of an empty list to be 0.

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