Numpy 子数组影响原始二维数组

Question

I created this 2D array with numpy :

>>>import numpy as np
>>>np.random.seed(0)
>>>x2 = np.random.randint(10, size=(3, 4))
>>>print(x2)
[[5 0 3 3]
 [7 9 3 5]
 [2 4 7 6]]

Then I created another subarray from x2

>>>x2_sub = x2[:2, :2]
>>>print(x2_sub)
[[5 0]
 [7 9]]

Now if I modify this subarray, the original array is changed:!:

>>>x2_sub[0, 0] = 99
>>>print(x2_sub)
[[99 0]
 [7 9]]
>>>print(x2)
[[99  0  3  3]
 [ 7  9  3  5]
 [ 2  4  7  6]]

I don't want the original array to change. Can anyone tell me what I'm doing worng?

Answer 1

Slices in numpy create a view unlike Python lists. Use .copy() to explicitly create a copy:

x2_sub = x2[:2, :2].copy()