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2D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 ,所以我不想将列表列表转换为numpy数组,然后使用[:,1]语法.我尝试在正常的列表列表上使用它,但显示错误,因此是不可能的.我正在为列表列表请求类似的东西,而不必遍历每个元素(在numpy数组中,使用[:,1]语法访问列比在数组元素上迭代要快).
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,但是再次建议在没有快捷方式的情况下遍历元素.
I found this link but again it suggests iterating over elements without a shortcut.
谢谢.
推荐答案
使用列表列表时,列表理解是您的朋友:
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]
还有一个方便的成语"用于转换嵌套列表,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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