How to crop a numpy 2d array to non-zero values?

Question

Let's say i have a 2d boolean numpy array like this:

import numpy as np
a = np.array([
    [0,0,0,0,0,0],
    [0,1,0,1,0,0],
    [0,1,1,0,0,0],
    [0,0,0,0,0,0],
], dtype=bool)

How can i in general crop it to the smallest box (rectangle, kernel) that includes all True values?

So in the example above:

b = np.array([
    [1,0,1],
    [1,1,0],
], dtype=bool)

Answer 1

After some more fiddling with this, i actually found a solution myself:

coords = np.argwhere(a)
x_min, y_min = coords.min(axis=0)
x_max, y_max = coords.max(axis=0)
b = cropped = a[x_min:x_max+1, y_min:y_max+1]

The above works for boolean arrays out of the box. In case you have other conditions like a threshold t and want to crop to values larger than t, simply modify the first line:

coords = np.argwhere(a > t)