How would I succinctly transpose nested lists?

Question

I am writing code to parse a tilemap map from a config file. The map is in the format:

1|2|3|4
1|2|3|4
2|3|4|5

where the numbers represent tiles. I then make this into an integer array:

[[int(tile) for tile in row.split("|")] for row in  "1|2|3|4\n1|2|3|4\n2|3|4|5".lstrip("\n").split("\n")]

This produces an array in the format [row][column], but I would prefer it to be [column][row] as in [x][y] so I wouldn't have to address it backwards (i.e. [y][x]). But I can't think of any concise ways of attacking the problem. I have considered reworking the format using xml syntax through Tiled, but it appears too difficult for a beginner.

Thanks in advance for any responses.

Answer 1

use mylist = zip(*mylist):

>>> original = [[1, 2, 3, 4], [1, 2, 3, 4], [2, 3, 4, 5]]
>>> transposed = zip(*original)
>>> transposed
    [(1, 1, 2), (2, 2, 3), (3, 3, 4), (4, 4, 5)]

>>> original[2][3]
    5

>>> transposed[3][2]
    5  

How it works: zip(*original) is equal to zip(original[0], original[1], original[2]). which in turn is equal to: zip([1, 2, 3, 4], [1, 2, 3, 4], [2, 3, 4, 5]).