TypeError: Invalid dimensions for image data when plotting array with imshow()

There is a (somewhat) related question on StackOverflow:

• Showing an image with pylab.imshow()

Here the problem was that an array of shape (nx,ny,1) is still considered a 3D array, and must be squeezed or sliced into a 2D array.

More generally, the reason for the Exception

TypeError: Invalid dimensions for image data

is shown here: matplotlib.pyplot.imshow() needs a 2D array, or a 3D array with the third dimension being of shape 3 or 4!

You can easily check this with (these checks are done by imshow, this function is only meant to give a more specific message in case it's not a valid input):

from __future__ import print_functionimport numpy as npdef valid_imshow_data(data):    data = np.asarray(data)    if data.ndim == 2:        return True    elif data.ndim == 3:        if 3 <= data.shape[2] <= 4:            return True        else:            print('The "data" has 3 dimensions but the last dimension '                  'must have a length of 3 (RGB) or 4 (RGBA), not "{}".'                  ''.format(data.shape[2]))            return False    else:        print('To visualize an image the data must be 2 dimensional or '              '3 dimensional, not "{}".'              ''.format(data.ndim))        return False

In your case:

>>> new_SN_map = np.array([1,2,3])>>> valid_imshow_data(new_SN_map)To visualize an image the data must be 2 dimensional or 3 dimensional, not "1".False

The np.asarray is what is done internally by matplotlib.pyplot.imshow so it's generally best you do it too. If you have a numpy array it's obsolete but if not (for example a list) it's necessary.

In your specific case you got a 1D array, so you need to add a dimension with np.expand_dims()

import matplotlib.pyplot as plta = np.array([1,2,3,4,5])a = np.expand_dims(a, axis=0)  # or axis=1plt.imshow(a)plt.show()

or just use something that accepts 1D arrays like plot:

a = np.array([1,2,3,4,5])plt.plot(a)plt.show()