如何在python中访问列表列表中的列 [英] How to access a column in a list of lists in python

问题描述

我在 python 中有一个由列表列表建模的二维数组，我想提取该列.我进行了快速研究，发现了一种使用 numpy 数组的方法.问题是 我不想使用 numpy 所以我不想将我的列表列表转换为一个 numpy 数组，然后使用 [:,1] 语法.我尝试在正常的列表列表中使用它，但它显示了一个错误，所以这是不可能的.我要求对列表列表进行类似的操作，而不必遍历每个元素(在 numpy 数组中，使用 [:,1] 语法访问列比遍历数组元素更快).

I have a 2D array in python modeled by a list of lists and I want to extract the column. I made a quick research and I found a way that uses numpy arrays. The problem is that I do not want to use numpy so I don't want to convert my list of lists into a numpy array and then use [:,1] syntax. I tried using it on a normal list of lists but it shows an error so it's not possible. I am asking for a similar thing for list of lists without having to go through each element(In numpy arrays, it's faster to access a column by using [:,1] syntax than iterating over the elements of the array).

我找到了这个链接但是它再次建议在没有快捷方式的情况下迭代元素.

I found this link but again it suggests iterating over elements without a shortcut.

提前致谢.

推荐答案

在处理列表列表时，列表推导式是您的朋友:

List comprehensions are your friend when working with lists of lists:

In [111]: alist
Out[111]: 
[[0, 1, 2, 3, 4, 5],
 [6, 7, 8, 9, 10, 11],
 [12, 13, 14, 15, 16, 17],
 [18, 19, 20, 21, 22, 23]]
In [112]: [row[1] for row in alist]
Out[112]: [1, 7, 13, 19]

还有一个方便的惯用语"用于转置嵌套列表，将列"转换为行":

There's also a handy 'idiom' for transposing a nested list, turning 'columns' into 'rows':

In [113]: tlist = list(zip(*alist))
In [114]: tlist
Out[114]: 
[(0, 6, 12, 18),
 (1, 7, 13, 19),
 (2, 8, 14, 20),
 (3, 9, 15, 21),
 (4, 10, 16, 22),
 (5, 11, 17, 23)]
In [115]: tlist[1]
Out[115]: (1, 7, 13, 19)

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