[FIXED] Conditional copy elements in numpy array

Issue

I want to copy elements from one numpy array to another while also checking condition e.g. if an element of B > 1. So, array A will be:

array([[None, None, None],
       [None, [4, 5], None],
       [None, None, None]])

and array B:

array([[0, 2, 2],
       [2, 2, 0],
       [0, 0, 0]])

I need array C to be

array([[None, [2], [2]],
       [[2], [2, 4, 5], None],
       [None, None, None]])

What is the most efficient way of doing that avoiding loops?

Solution

Use np.where:

a = np.array([None, [1,2], None])
b = np.array([0,1,2])
np.where(b>0, a, b)
>>array([None, 1, 2], dtype=object)

Alternative - If you want to modify in place, you can also use a boolean mask:

a = np.array([None, [1,2], None])
b = np.array([0,1,2])
m = b > 0
a[m] = b[m]
>>array([None, 1, 2], dtype=object)

Sidenote: arrays are not the best thing for that kind of data (see comments)

Answered By - Tarifazo