numpy中轴处理的实现

import numpy as np
 
a=np.array([1,2,3])
 
b=a[np.newaxis,:]
c=a[:,np.newaxis]

numpy.expand_dims(a,axis)

import numpy as np
 
a = np.arange(4).reshape(1, 4)
 
print(">>>")
print(a.shape)
print(a)
print()
 
b = np.broadcast_to(a, (4, 4))
print(">>>")
print(b.shape)
print(b)
 
>>>
(1, 4)
[[0 1 2 3]]
 
>>>
(4, 4)
[[0 1 2 3]
 [0 1 2 3]
 [0 1 2 3]
 [0 1 2 3]]

a = np.arange(24).reshape(2, 3, 4)
print(">>>")
print(a.shape)
print(a)
print()
 
roll = np.rollaxis(a, 2) # 把第2个轴滚动到0维位置
print(">>>")
print(roll.shape)
print(roll)
print()
 
roll2 = np.rollaxis(a, 2, 1) # 把第2个轴滚动到1维位置
print(">>>")
print(roll2.shape)
print(roll2)
print()
 
 
>>>
(2, 3, 4)
[[[ 0  1  2  3]
  [ 4  5  6  7]
  [ 8  9 10 11]]
 
 [[12 13 14 15]
  [16 17 18 19]
  [20 21 22 23]]]
 
>>>
(4, 2, 3)
[[[ 0  4  8]
  [12 16 20]]
 
 [[ 1  5  9]
  [13 17 21]]
 
 [[ 2  6 10]
  [14 18 22]]
 
 [[ 3  7 11]
  [15 19 23]]]
 
>>>
(2, 4, 3)
[[[ 0  4  8]
  [ 1  5  9]
  [ 2  6 10]
  [ 3  7 11]]
 
 [[12 16 20]
  [13 17 21]
  [14 18 22]
  [15 19 23]]]