Array 차원 확장, 축소

import numpy as np

arr = [[[2,1,1],[2,1,2]]]

expansion = np.expand_dims(arr, axis=0)
reduction = np.squeeze(arr, axis=1)

arr.shape, expansion.shape, reduction.shape

((3, 1), (1, 3, 1), (3,))

print(arr, expansion, reduction, sep='\n\n')

[[1],
[2],
[3]]

[[[1],
[2],
[3]]]

[1, 2, 3]