NumPy - How to broadcast arrays of different shapes
I have a 200 x 200 array of vectors. Its shape is (200, 200, 3).
I also have an array of 22 vectors. Its shape is (22,3).
I want to subtract all 22 vectors in the second array from each vector in the first array. The output should have shape (200, 200, 22, 3).
I'd like to perform an operation like
first - second
But I get the error
*** ValueError: operands could not be broadcast together with shapes (200,200,3) (22,3)
I think I need to pad the first array somehow in order to allow NumPy to broadcast the arrays together. How do I tell NumPy how to perform the broadcast?
numpy numpy-broadcasting numpy-ndarray
asked Nov 19 '18 at 21:15
bcattlebcattle
6,14443760
add a comment |
I have a 200 x 200 array of vectors. Its shape is (200, 200, 3).
I also have an array of 22 vectors. Its shape is (22,3).
I want to subtract all 22 vectors in the second array from each vector in the first array. The output should have shape (200, 200, 22, 3).
I'd like to perform an operation like
first - second
But I get the error
*** ValueError: operands could not be broadcast together with shapes (200,200,3) (22,3)
I think I need to pad the first array somehow in order to allow NumPy to broadcast the arrays together. How do I tell NumPy how to perform the broadcast?
numpy numpy-broadcasting numpy-ndarray
asked Nov 19 '18 at 21:15
bcattlebcattle
6,14443760
Doesn't subtracting 3D vectors produce another 3D vector? How is the output shape (200, 200, 22)? Shoudn't it be (200, 200, 22, 3)?
– eozd
Nov 19 '18 at 21:22
You're right, fixed.
– bcattle
Nov 19 '18 at 21:23
3
first[:,:,None,:] - second; or to be a bit more explicitfirst[:,:,None,:] - second[None,None,:,:]. In other words imagine where the two arrays have to be expanded to fit in the target (200,200,22,3) array.
– hpaulj
Nov 19 '18 at 21:24
Works beautifully, thanks
– bcattle
Nov 19 '18 at 21:28
add a comment |
I have a 200 x 200 array of vectors. Its shape is (200, 200, 3).
I also have an array of 22 vectors. Its shape is (22,3).
I want to subtract all 22 vectors in the second array from each vector in the first array. The output should have shape (200, 200, 22, 3).
I'd like to perform an operation like
first - second
But I get the error
*** ValueError: operands could not be broadcast together with shapes (200,200,3) (22,3)
I think I need to pad the first array somehow in order to allow NumPy to broadcast the arrays together. How do I tell NumPy how to perform the broadcast?
numpy numpy-broadcasting numpy-ndarray
asked Nov 19 '18 at 21:15
bcattlebcattle
6,14443760
I have a 200 x 200 array of vectors. Its shape is (200, 200, 3).
I also have an array of 22 vectors. Its shape is (22,3).
I want to subtract all 22 vectors in the second array from each vector in the first array. The output should have shape (200, 200, 22, 3).
I'd like to perform an operation like
first - second
But I get the error
*** ValueError: operands could not be broadcast together with shapes (200,200,3) (22,3)
I think I need to pad the first array somehow in order to allow NumPy to broadcast the arrays together. How do I tell NumPy how to perform the broadcast?
numpy numpy-broadcasting numpy-ndarray
numpy numpy-broadcasting numpy-ndarray
asked Nov 19 '18 at 21:15
bcattlebcattle
6,14443760
asked Nov 19 '18 at 21:15
bcattlebcattle
6,14443760
edited Nov 19 '18 at 21:23
bcattle
asked Nov 19 '18 at 21:15
bcattlebcattle
6,14443760
asked Nov 19 '18 at 21:15
bcattlebcattle
6,14443760
asked Nov 19 '18 at 21:15
bcattlebcattle
6,14443760
6,14443760
Doesn't subtracting 3D vectors produce another 3D vector? How is the output shape (200, 200, 22)? Shoudn't it be (200, 200, 22, 3)?
– eozd
Nov 19 '18 at 21:22
You're right, fixed.
– bcattle
Nov 19 '18 at 21:23
3
first[:,:,None,:] - second; or to be a bit more explicitfirst[:,:,None,:] - second[None,None,:,:]. In other words imagine where the two arrays have to be expanded to fit in the target (200,200,22,3) array.
– hpaulj
Nov 19 '18 at 21:24
Works beautifully, thanks
– bcattle
Nov 19 '18 at 21:28
add a comment |
Doesn't subtracting 3D vectors produce another 3D vector? How is the output shape (200, 200, 22)? Shoudn't it be (200, 200, 22, 3)?
– eozd
Nov 19 '18 at 21:22
You're right, fixed.
– bcattle
Nov 19 '18 at 21:23
3
first[:,:,None,:] - second; or to be a bit more explicitfirst[:,:,None,:] - second[None,None,:,:]. In other words imagine where the two arrays have to be expanded to fit in the target (200,200,22,3) array.
– hpaulj
Nov 19 '18 at 21:24
Works beautifully, thanks
– bcattle
Nov 19 '18 at 21:28
Doesn't subtracting 3D vectors produce another 3D vector? How is the output shape (200, 200, 22)? Shoudn't it be (200, 200, 22, 3)?
– eozd
Nov 19 '18 at 21:22
Doesn't subtracting 3D vectors produce another 3D vector? How is the output shape (200, 200, 22)? Shoudn't it be (200, 200, 22, 3)?
– eozd
Nov 19 '18 at 21:22
You're right, fixed.
– bcattle
Nov 19 '18 at 21:23
You're right, fixed.
– bcattle
Nov 19 '18 at 21:23
3
3
first[:,:,None,:] - second; or to be a bit more explicit first[:,:,None,:] - second[None,None,:,:]. In other words imagine where the two arrays have to be expanded to fit in the target (200,200,22,3) array.– hpaulj
Nov 19 '18 at 21:24
first[:,:,None,:] - second; or to be a bit more explicit first[:,:,None,:] - second[None,None,:,:]. In other words imagine where the two arrays have to be expanded to fit in the target (200,200,22,3) array.– hpaulj
Nov 19 '18 at 21:24
Works beautifully, thanks
– bcattle
Nov 19 '18 at 21:28
Works beautifully, thanks
– bcattle
Nov 19 '18 at 21:28
add a comment |
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Doesn't subtracting 3D vectors produce another 3D vector? How is the output shape (200, 200, 22)? Shoudn't it be (200, 200, 22, 3)?
– eozd
Nov 19 '18 at 21:22
You're right, fixed.
– bcattle
Nov 19 '18 at 21:23
3
first[:,:,None,:] - second; or to be a bit more explicitfirst[:,:,None,:] - second[None,None,:,:]. In other words imagine where the two arrays have to be expanded to fit in the target (200,200,22,3) array.– hpaulj
Nov 19 '18 at 21:24
Works beautifully, thanks
– bcattle
Nov 19 '18 at 21:28