numpy expand_dims and newaxis

发表于 | 更新于 | 分类于 | 评论数：

expand_dims

在数组的某个维度增加一个为1的维度。

代码示例

代码地址

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
import numpy as np


a = np.ones([2, 3, 4])
print(a.shape)

a1 = np.expand_dims(a, 0)
print(a1.shape)

a2 = np.expand_dims(a, 1)
print(a2.shape)

a3 = np.expand_dims(a, 2)
print(a3.shape)

a4 = np.expand_dims(a, 3)
print(a4.shape)

newaxis

简介

newaxis就是None的一个alias

1
2
>>> np.newaxis is None
True

用途

常用于slicing。用于给数组增加一个维度。

代码示例

代码地址

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
a = np.ones((2, 3, 4))
print(a.shape)
(2, 3, 4)

a1 = a[np.newaxis]
print(a1.shape)
(1, 2, 3, 4)

a2 = a[:, np.newaxis]
print(a2.shape)
(2, 1, 3, 4)

a3 = a[:, :, np.newaxis]
print(a3.shape)
(2, 3, 1, 4)

a4 = a[:, :, :, np.newaxis]
print(a4.shape)
(2, 3, 4, 1)

a5 = a[:, :, np.newaxis, np.newaxis, :]
print(a5.shape)
(2, 3, 1, 1, 4)

参考文献

1.https://stackoverflow.com/questions/29241056/how-does-numpy-newaxis-work-and-when-to-use-it