Loop through 2D array in reverse

Question

I want to go through a 2D array in reverse. Thats is why I use reversed() but I get an error that says

list indices must be integers, not list

Array example:

labirynth = [
[1,1,1,1,1,1,1],
[1,0,0,0,1,0,1],
[1,0,1,0,0,0,1],
[1,1,1,1,1,1,1]
]

My current solution:

for i in reversed(labirynth):
    for j in reversed(labirynth[i]):
        #do stuff

Possible duplicate of [Rotating a two-dimensional array in Python](https://stackoverflow.com/questions/8421337/rotating-a-two-dimensional-array-in-python) — Torxed, Sep 28 '17 at 08:34

score 1 · Accepted Answer · answered Sep 28 '17 at 08:36

1

There is no need to access the list with []. The outer for loop already returns the list. You can just do

for i in reversed(labirynth):
    for j in reversed(i):
        # do stuf...

answered Sep 28 '17 at 08:36

bgfvdu3w

1,548
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17

score 0 · Answer 2 · answered Sep 28 '17 at 08:38

You probably want

for i in reversed(labirynth):
  for j in reversed(i):
    # do stuff

here's an interactive demo:

>>> labirynth = [
[1,1,1,1,1,1,1],
[1,0,0,0,1,0,1],
[1,0,1,0,0,0,1],
[1,1,1,1,1,1,1]
]
... ... ... ... ...
>>> for i in reversed(labirynth):
...    print i
... 
[1, 1, 1, 1, 1, 1, 1]
[1, 0, 1, 0, 0, 0, 1]
[1, 0, 0, 0, 1, 0, 1]
[1, 1, 1, 1, 1, 1, 1]
>>> for i in reversed(labirynth):
...   for j in reversed(i):
...     print j
... 
1
1
1
... continues

That precisely solves my problem. Thank you for such good explanation! — Uliysess, Sep 28 '17 at 08:40

Loop through 2D array in reverse

2 Answers2