Shuffle columns of an array with Numpy

Question

Let's say I have an array r of dimension (n, m). I would like to shuffle the columns of that array.

If I use numpy.random.shuffle(r) it shuffles the lines. How can I only shuffle the columns? So that the first column become the second one and the third the first, etc, randomly.

Example:

input:

array([[  1,  20, 100],        [  2,  31, 401],        [  8,  11, 108]]) 

output:

array([[  20, 1, 100],        [  31, 2, 401],        [  11,  8, 108]]) 

Answer 1

One approach is to shuffle the transposed array:

 np.random.shuffle(np.transpose(r)) 

Another approach (see YXD's answer https://stackoverflow.com/a/20546567/1787973) is to generate a list of permutations to retrieve the columns in that order:

 r = r[:, np.random.permutation(r.shape[1])] 

Performance-wise, the second approach is faster.