How to use `np.vectorize()` when mapping between different dimensions

np_vectorize.py

import numpy as np

# reduce dimension
mapping1 = {
    (1, 2): 0,
    (3, 4): 1,
    (5, 6): 2,
}
def mapper1(m1, m2):
    return mapping1.get((m1, m2))

a = np.array([[1, 2], [3, 4], [5, 6]])
b = np.vectorize(mapper1)(a[:, 0], a[:, 1])

print(b)

# extend dimension
mapping2 = {
    0: [1, 2],
    1: [3, 4],
    2: [5, 6],
}

a = np.array([0, 1, 2])
b = np.array(np.vectorize(mapping2.get, otypes=[list])(a).tolist())

print(b)