Problem with rotating a two-dimensional array in python [duplicate]

Question

How to to make this array rotate by 90 degrees to right without using numpy.

multiarray = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
auxiliaryArray = []
colLength = len(multiarray[0])
rowLength = len(multiarray)
for indexRow in range(len(multiarray)):
    for indexCol in range(len(multiarray[0])):
        auxiliaryArray[indexCol][rowLength - 1 - indexRow] = multiarray[indexRow][indexCol]

print(auxiliaryArray)

Error: IndexError: list index out of range

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

instead of making an empty list, initialize a list with zeroes or some other values, that way you can't get out of range error — Mahrkeenerh
– Mahrkeenerh, Commented Nov 4, 2021 at 16:49
if you are looking at mathematic way without using additional library you can read this. integratedmlai.com/matrixinverse — Shahin Shirazi
– Shahin Shirazi, Commented Nov 4, 2021 at 16:53

mozway · Accepted Answer · 2021-11-04 16:49:08Z

0

You can use zip on the reversed array:

auxiliaryArray = list(zip(*multiarray[::-1]))

or

auxiliaryArray = list(zip(*reversed(multiarray)))

output: [(7, 4, 1), (8, 5, 2), (9, 6, 3)]

If you need lists and not tuples:

auxiliaryArray = list(map(list, zip(*reversed(multiarray))))

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

answered Nov 4, 2021 at 16:49

mozway

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4 Comments

Zukashi Over a year ago

Could it be done with append?

mozway Over a year ago

Why? Is this an assignment?

Zukashi Over a year ago

Something like that

mozway Over a year ago

I take this as a yes… Yes it can be done, but you should have made it explicit from the beginning that it was an assignment (cf. SO guidelines), your question wouldn't have been closed

Serge de Gosson de Varennes · Accepted Answer · 2021-11-04 16:50:58Z

0

This does it:

list(zip(*multiarray[::-1]))

answered Nov 4, 2021 at 16:50

Serge de Gosson de Varennes

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