如何在python中访问列表列表中的列
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How to access a column in a list of lists in python
提问by Oussama Boussif
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 numpyso 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，所以我不想将列表列表转换为 numpy 数组，然后使用 [:,1] 语法。我尝试在普通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 found this linkbut again it suggests iterating over elements without a shortcut.
我找到了这个链接，但它再次建议在没有快捷方式的情况下迭代元素。
Thanks in advance.
提前致谢。
回答by hpaulj
List comprehensions are your friend when working with lists of lists:
在处理列表列表时，列表推导式是您的朋友：
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]
There's also a handy 'idiom' for transposing a nested list, turning 'columns' into 'rows':
还有一个方便的“惯用语”用于转置嵌套列表，将“列”转换为“行”：
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)
