Reversing arrays in 2D arrays in Python

Question

I have a question wether it is possible to reverse certain arrays in my 2D array. For example

a=[[1,2],[3,4],[5,6]] 
a[1:3].reverse()
print(a)

would output:

[1,2],[5,6],[3,4]

I hope you can help :)

RafalS · Accepted Answer · 2019-12-02 20:37:31Z

2

a = [[1, 2], [3, 4], [5, 6]]
a = a[:1] + list(reversed(a[1:3]))
print(a)

You could also use pure slicing, but imo the previous version is more readable:

a = a[:1] + a[:-3:-1]

answered Dec 2, 2019 at 20:31

RafalS

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1 Comment

to add explanation, a[1:3] creates a new list and because .reverse is an in-place method - a is not affected

Teslavolt · Accepted Answer · 2019-12-02 20:59:47Z

0

Your code is actually reversing a copy, and not changing the underlying array.

I'd do this:

a[1:3] = reversed(a[1:3])

It takes a reversed copy of the elements from 1 to three and puts them into their initial locations.

answered Dec 2, 2019 at 20:59

Teslavolt

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