a = np.array([1, 2, 3])
aa = np.array([1], [2], [3])
b = np.array([1, 2, 3])
bb = np.array([1], [2], [3])
np.concatenate((a, b), axis = 1)
array([1, 2, 3, 1, 2, 3])     # It's ok, that's what I was expecting
np.concatenate((a, b), axis = 0)
array([1, 2, 3, 1, 2, 3])     # It's not ok, that's not what I was expecting

Yo estaba esperando:

array([[1, 2, 3],
       [1, 2, 3]])

incluso con aa y bb obtengo la misma inconsistencia. Entonces, ¿hay una solución simple para concatenar a lo largo del eje 0 dos matrices unidimensionales?