np.newaxis先明確功能:增加一個維度
in1:
a=np.array([1,2,3,4,5])
print (a.shape)
print (a)
out1:
(5,)
[1 2 3 4 5]
in2:
a=np.array([1,2,3,4,5])
b=a[np.newaxis,:]
print (a.shape,b.shape)
print (a)
print (b)
out2:
(5,) (1, 5)
[1 2 3 4 5]
[[1 2 3 4 5]]
in3:
a=np.array([1,2,3,4,5])
b=a[:,np.newaxis]
print (a.shape,b.shape)
print (a)
print (b)
out3:
(5,) (5, 1)
[1 2 3 4 5]
[[1]
[2]
[3]
[4]
[5]]
總結
- 數據往往是一維,不能滿足矩陣相乘的前提條件,以此需要np.newaxis
- np.newaxis在左,稱”1行n列“,在右,稱”n行1列“(在哪哪爲1)