How can I extract all columns and diagonal from a list of lists in python?

Question

I have a list of lists, for example:

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

I need to get this:

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

And I also need to get the diagonal. I'd preferably need to do this without importing other libraries.

Any reason for not using libraries? This is an easy one liner with numpy transpose. — pykam, Feb 11 '21 at 13:56
Possible duplicate of https://stackoverflow.com/questions/6473679/transpose-list-of-lists — gmdev, Feb 11 '21 at 13:56
Yes, I didn't really know how to word that, but I'd like to do it without using numpy — Mario Santoro, Feb 11 '21 at 13:56

Baruch Gans · Answer 1 · 2021-02-11T17:26:13.800

2

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

[list(i) for i in zip(*arr)]

output:

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

To get the diagonal:

[arr[x][x] for x in range(len(arr))]

output:

[1, 5, 9]

edited Feb 11 '21 at 17:26

answered Feb 11 '21 at 13:57

Baruch Gans

1 Answers1