I have two numpy arrays:
a = np.array([[0,0,1],
[0,1,0],
[0,1,1],
[1,1,1],
[1,1,0],
[0,0,0]])
b = np.array([9,9,9])
What is the easiest way to append array b into each row of array a?
The output should look like this:
c = np.array([[0,0,1,9,9,9],
[0,1,0,9,9,9],
[0,1,1,9,9,9],
[1,1,1,9,9,9],
[1,1,0,9,9,9],
[0,0,0,9,9,9]])
One way using broadcast_to and hstack:
c = np.hstack([a, np.broadcast_to(b, (a.shape[0], b.shape[0]))])
output:
array([[0, 0, 1, 9, 9, 9],
[0, 1, 0, 9, 9, 9],
[0, 1, 1, 9, 9, 9],
[1, 1, 1, 9, 9, 9],
[1, 1, 0, 9, 9, 9],
[0, 0, 0, 9, 9, 9]])
One way to expand array b and then append to array a
>>> np.append(a, b.repeat(len(a)).reshape((len(a),len(b))), axis=1)
array([[0, 0, 1, 9, 9, 9],
[0, 1, 0, 9, 9, 9],
[0, 1, 1, 9, 9, 9],
[1, 1, 1, 9, 9, 9],
[1, 1, 0, 9, 9, 9],
[0, 0, 0, 9, 9, 9]])
Another possible solution, using list comprehension:
np.array([x + b.tolist() for x in a.tolist()])
Output:
array([[0, 0, 1, 9, 9, 9],
[0, 1, 0, 9, 9, 9],
[0, 1, 1, 9, 9, 9],
[1, 1, 1, 9, 9, 9],
[1, 1, 0, 9, 9, 9],
[0, 0, 0, 9, 9, 9]])
Yet another possible solution, using numpy.fromiter and chain.from_iterable:
from itertools import chain
(np.fromiter(chain.from_iterable(np.concatenate((x, b)) for x in a), int)
.reshape((a.shape[0], a.shape[1] + b.shape[0])))
