How to assign from a source array being a subset of the destination array?

Question

Having two arrays like:

a = np.zeros((3, 4), dtype=int)
[[0 0 0 0]
 [0 0 0 0]
 [0 0 0 0]]

b = np.ones((2, 3), dtype=int)
[[1 1 1]
 [1 1 1]]

How to assign from a source array (b) to the entries in the destination array (a) that are present in source ?

The resulting array should then be:

[[1 1 1 0]
 [1 1 1 0]
 [0 0 0 0]]

Answer 1

You can simply obtain the shape of b like:

m,n = b.shape

and then use slices to set the elements in a:

a[:m,:n] = b

This generates:

>>> m,n = b.shape
>>> a[:m,:n] = b
>>> a
array([[1, 1, 1, 0],
       [1, 1, 1, 0],
       [0, 0, 0, 0]])

In case a and b have the same but an arbitrary number of dimensions, we can use the following generator:

a[tuple(slice(mi) for mi in b.shape)] = b

which results again in:

>>> a[tuple(slice(mi) for mi in b.shape)] = b
>>> a
array([[1, 1, 1, 0],
       [1, 1, 1, 0],
       [0, 0, 0, 0]])

But this will also work for 3d, 4d, ... arrays.

Answer 2

Get the shape of array to be assigned and then slice the destination array and assign -

m,n = b.shape
a[:m,:n] = b