I have a 2D numpy array.

x = np.arange(25).reshape(5, 5)

I need to create a mask by index condition. For example elements with even indexes.

mask = np.zeros((5, 5), dtype=bool)

for i in range(5):
    for j in range(5):
        if i % 2 == 0 and j % 2 == 0:
            mask[i][j] = True

Is there a way to create such a mask using numpy tools?

CodePudding user response：

Replace your nested loops with this:

mask[::2,::2] = True 

The ::2 means "from beginning to end, for every second element" in each axis.