Question

I am looking for a way to rotate a plot generated in matplotlib-pyplot (Python libraries) by 45 degrees (so that instead of a square shape you would have a diamond shape, for example), anyone know if this can be done?

One way I can think of is to use a rotation filter on all the data so that it appears rotated, but then the plot itself will still be in the original orientation.

I want to be able to use the matplotlib interactive features, so saving as an image and then rotating won’t work.

Also, I want to use pyplot functions to draw the plot, so using a different library for the plotting is not an ideal solution.

Answer 1

Ok so currently the only partial solution I found is to apply a rotation to the plot. This allows to use the interactive interface that matplotlib/pyplot offers.

For dot plots like plot() and scatter() this is trivial, but I was specifically interested in rotating imshow(). This link discusses the transform keyword that could have potentially been used for this task, but it is apparently not working.

Fortunately, I found a workaround using pcolormesh(). pcolormesh() plots a quadrilateral mesh and allows you to specify the corner coordinates. So, the answer is to just apply the relevant transformations to the corner coordinates. Note however, that pcolormesh() works a bit different than imshow – it plots your matrix flipped.

I haven’t seen this solution anywhere on the web, so here is some code for pcolormesh()/imshow() rotated by 45 degrees:

import matplotlib.pyplot as plt
import numpy as np

def pcolormesh_45deg(C):

    n = C.shape[0]
    # create rotation/scaling matrix
    t = np.array([[1,0.5],[-1,0.5]])
    # create coordinate matrix and transform it
    A = np.dot(np.array([(i[1],i[0]) for i in itertools.product(range(n,-1,-1),range(0,n+1,1))]),t)
    # plot
    plt.pcolormesh(A[:,1].reshape(n+1,n+1),A[:,0].reshape(n+1,n+1),np.flipud(C))