CODEWITHSUNDEEP
pythonpython-3.xmatrix
user3456217
user3456217

Reputation: 9

Reverse rows of n*n matrix

I have a matrix [[1 2 3],[4,5,6],[7,8,9]] How can I reverse it horizontally so it become [[3 2 1],[6,5,4],[9,8,7]]

Upvotes: 0

Views: 384

Answers (3)

Akhilesh Pandey
Akhilesh Pandey

Reputation: 896

You can try this out:

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

# take each list in the list of lists l and reverse that in-place
for item in l:
    item.reverse()

print(l)

output: 

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

This is in-place conversion, so no need to create any temporary variables to store values in the inter-mediate steps.

Upvotes: 0

ggorlen
ggorlen

Reputation: 57115

You can use a list comprehension as follows:

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

print([list(reversed(x)) for x in m])

Output:

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

Upvotes: 0

NPE
NPE

Reputation: 500663

If a is your matrix (represented as in your question), the following will flip it horizontally:

map(list.reverse, a)

This will change it in place. If you'd rather create a new matrix:

b = [row[::-1] for row in a]

If you deal with matrices a lot, I'd recommend that you take a look at NumPy. It has a lot of numerical primitives and is very widely used.

Upvotes: 5

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