[英]Multiplying column and row vectors from numpy 2d array with a scalars form a different 1d array
How to multiply each column vector with a scalar from an array? 如何将每个列向量与数组中的标量相乘?
Example 例
a b c x1a x2b x3c
a b c x1 x2 x3 -> x1a x2b x3c
a b c x1a x2b x3c
a b c x1a x2b x3c
How to multiply each row vector with a scalar from an array? 如何将每个行向量与数组中的标量相乘?
Example 例
a a a a x1a x1a x1a x1a
b b b b x1 x2 x3 -> x2b x2b x2b x2b
c c c c x3c x3c x3c x3c
Recommendations for a better topic will be appreciated 有关更好主题的建议将不胜感激
I prefer the following syntax, which is short, but explicit 我更喜欢以下语法,它很简短但很明确
A = np.ones((3,4))
B = np.arange(3)
print A * B[:,None]
>>> array([[ 0., 0., 0., 0.],
[ 1., 1., 1., 1.],
[ 2., 2., 2., 2.]])
A = np.ones((4,3))
B = np.arange(3)
print A * B[None,:]
>>> array([[ 0., 1., 2.],
[ 0., 1., 2.],
[ 0., 1., 2.],
[ 0., 1., 2.]])
1. Column multiplication 1.列乘法
In [39]: A = array([[1,2,3],[1,2,3],[1,2,3],[1,2,3]])
In [40]: X = array([10,20,30])
In [41]: A
Out[41]:
array([[1, 2, 3],
[1, 2, 3],
[1, 2, 3],
[1, 2, 3]])
In [42]: X
Out[42]: array([10, 20, 30])
In [43]: A * X
Out[43]:
array([[10, 40, 90],
[10, 40, 90],
[10, 40, 90],
[10, 40, 90]])
1. Row multiplication 1.行乘法
In [44]: B = array([[1,1,1,1],[2,2,2,2],[3,3,3,3]])
In [45]: B
Out[45]:
array([[1, 1, 1, 1],
[2, 2, 2, 2],
[3, 3, 3, 3]])
In [46]: X = array([10,20,30])
In [47]: X
Out[47]: array([10, 20, 30])
In [48]: (B.transpose() * X).transpose()
Out[48]:
array([[10, 10, 10, 10],
[40, 40, 40, 40],
[90, 90, 90, 90]])
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