How to slice a nested list twice?-CodePudding

With a nested list like:

ex_list = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]

I need to be able to slice this list for:

[[1, 2], [4, 5]]

I've been trying:

list(ex_list[:2][:2])

but this isn't working. I'm obviously doing something very wrong but haven't been able to find a solution as using commas doesn't work either for some reason.

CodePudding user response：

You need to slice the elements seperately to the outer list, better to do the outer list first to avoid unnecessary inner slices

[inner[:2] for inner in ex_list[:2]]

CodePudding user response：

You should try using comprehension: Try:

[i[:2] for i in ex_list[:2]]

Code:

ex_list = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
print([i[:2] for i in ex_list[:2]])

Output:

[[1, 2], [4, 5]]

CodePudding user response：

Is using numpy an option?

import numpy as np

ex_list = np.array([[1, 2, 3], [4, 5, 6], [7, 8, 9]])
print(ex_list[:2,:2].tolist()) # [[1, 2], [4, 5]]

The first :2 slice the outer list, the second slice each one of the inner lists.