CODEWITHSUNDEEP
pythonarraysnumpy
Guanxiong.Liu
Guanxiong.Liu

Reputation: 27

how can I do 2d 3d multiplication

I have two array one is 3d : 

np.array([[[1,2,3],[3,2,1]],
          [[2,3,2],[1,2,5]]])

and one 2d array : 

np.array([[2,3],
          [3,4]])

and I want to multiply these two to get 

np.array([[[2,4,6],[9,6,3]],
          [[6,9,6],[4,8,20]]])

How can I do this using numpy package? Thanks.

Upvotes: 2

Views: 68

Answers (2)

rnso
rnso

Reputation: 24535

With following names:

main = np.array([[[1,2,3],[3,2,1]],
                 [[2,3,2],[1,2,5]]])
fac = np.array([[2,3],
                [3,4]])

It can managed with iteration as follows:

a1 = []
for i in [0,1]:
    a2 = []
    for j in [0,1]:
            a2.append(main[i][j]*fac[i][j]) 
    a1.append(a2)

print(a1)

Output:

[[array([2, 4, 6]), array([9, 6, 3])], [array([6, 9, 6]), array([ 4,  8, 20])]]

Upvotes: 0

Kasravnd
Kasravnd

Reputation: 107287

Use broadcasting:

In [129]: b[:,:,None] * a
Out[129]: 
array([[[ 2,  4,  6],
        [ 9,  6,  3]],

       [[ 6,  9,  6],
        [ 4,  8, 20]]])

Upvotes: 3

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