Reverse a string within a list and further reverse the list within a nested list

Question

I have a multidimensional list which is basically a list of strings nested within a list. I want a list to be reversed and also the list items within the list to be reverse and further the strings in the list should also be reversed.

Ex: I have a list

[
    ['123', '456', '789'], 
    ['234', '567', '890'], 
    ['345', '678', '901']
]

I want the result to be

[
    ['109', '876', '543'],
    ['098', '765', '432'],
    ['987', '654', '321']
]

I've already tried the code, It's working. But can we simplify further using list comprehension.

Below is the code which I tried.

old = [['123', '456', '789'], ['234', '567', '890'], ['345', '678', '901']]
new = [];
for x in old[::-1]:
    z = [];
    for y in x:
        z.insert(0, y[::-1])
    new.append(z)
print(new)

Input

[['123', '456', '789'], ['234', '567', '890'], ['345', '678', '901']]

Output

[['109', '876', '543'], ['098', '765', '432'], ['987', '654', '321']]

you don't need the semicolons at the ends of the line :)

Jean-François Fabre
– Jean-François Fabre ♦

2018-12-21 09:49:58 +00:00
Commented Dec 21, 2018 at 9:49 — Jean-François Fabre
– Jean-François Fabre ♦, Commented Dec 21, 2018 at 9:49

Jean-François Fabre · Accepted Answer · 2018-12-21 10:00:38Z

5

you want this one-liner:

result = [[x[::-1] for x in reversed(y)] for y in reversed(lst)]

notes:

reversed(lst) is faster than lst[::-1] because it doesn't create a new list, it just iterates backwards (in that case it works because the length is known).
x[::-1] is left as-is because it's much faster than "".join(reversed(x)) to reverse a string as a string.

edited Dec 21, 2018 at 10:00

answered Dec 21, 2018 at 9:43

Jean-François Fabre♦

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2 Comments

Stupid Dream Over a year ago

Thanks, I was able to modify it after your solution result = [[x[::-1] for x in y[::-1]] for y in lst[::-1]]

Jean-François Fabre Over a year ago

yeah works too, but reversed is better [::-1] creates a new list (allocation, copy...) that you don't need.

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