How do you rotate a two dimensional array?

Question

Inspired by Raymond Chen\'s post, say you have a 4x4 two dimensional array, write a function that rotates it 90 degrees. Raymond links to a solution in pseudo code, but I\'d

Answer 1

Python:

rotated = list(zip(*original[::-1]))

and counterclockwise:

rotated_ccw = list(zip(*original))[::-1]

How this works:

zip(*original) will swap axes of 2d arrays by stacking corresponding items from lists into new lists. (The * operator tells the function to distribute the contained lists into arguments)

>>> list(zip(*[[1,2,3],[4,5,6],[7,8,9]]))
[[1,4,7],[2,5,8],[3,6,9]]

The [::-1] statement reverses array elements (please see Extended Slices or this question):

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

Finally, combining the two will result in the rotation transformation.

The change in placement of [::-1] will reverse lists in different levels of the matrix.