python - Numpy 随机选择不适用于二维列表

Question

我运行了以下 python 代码:

import numpy as np
a_list = [[1, 2, 3], [4, 5, 6], [7, 8, 9], [10, 1, 2]]
np.random.choice(a_list, size=20, 
    replace=True)

期待这样的结果:

[[7, 8, 9], [1, 2, 3], [4, 5, 6], [7, 8, 9], [10, 1, 2], [1, 2, 3], [1, 2, 3], [10, 1, 2], [1, 2, 3], [7, 8, 9], [1, 2, 3], [1, 2, 3], [10, 1, 2], [4, 5, 6], [4, 5, 6], [10, 1, 2], [10, 1, 2], [7, 8, 9], [1, 2, 3], [7, 8, 9]]

但我得到的却是下面的错误信息:

 ValueError                           Traceback (most recent call last)
 <ipython-input-80-c11957aca587> in <module>()
    2 a_list = [[1, 2, 3], [4, 5, 6], [7, 8, 9], [10, 1, 2]]
    3 np.random.choice(a_list, size=20, 
----> 4 replace=True)

mtrand.pyx in mtrand.RandomState.choice()

ValueError: a must be 1-dimensional

如何从二维列表中随机选择？

Answer 1

您将需要使用索引:

import numpy as np

arr = np.array([[1, 2, 3], [4, 5, 6], [7, 8, 9], [10, 1, 2]])
indices = np.arange(arr.shape[0])

output = arr[np.random.choice(indices, 20)]

或者，甚至更短(基于 hpaulj 的评论):

output = arr[np.random.choice(arr.shape[0],20)]