How to concatenate to a Tensor with a 0 dimension?

1

In Numpy I can do:

np.hstack((np.zeros((3, 0)), np.zeros((3, 3)))

and it would give me a 3x3 zero matrix.
But in pytorch,

torch.cat((torch.zeros(3, 0), torch.zeros(3, 3)), dim=1)

gives me a run time error RuntimeError: dim out of range - got 1 but the tensor is only 1D. Because torch.zeros(3, 0) is actually a 3-element Tensor (as opposed to Numpy, where it is empty).

Now, @smth has said before that there are no 0 dimensional Tensors in pytorch (For-loop with a 2D matrix of size 0) but does anyone know of a solution to this problem, where for example the 0 size of the dim is being calculated in a loop?

For example if I have

for i in xrange(5):
  print torch.cat((torch.zeros(3, i), torch.zeros(3, 3)), dim=1)

the first iteration would give an error…

2 Likes
2

Hi, have you found the solution?

4

Yes - apparently now (in version 0.3.0) you can create 0-dimensional tensors. For example,
torch.zeros(0, 0) will give [torch.FloatTensor with no dimension].

So now you can do torch.cat((torch.zeros(0, 0), torch.zeros(3, 3))).

3 Likes
5

You can also do torch.Tensor().

3 Likes
6

I do something like this to concatenate zero dimensional tensor to another tensor

A = torch.tensor([0]) # [0]
B = torch.tensor([1, 2, 3, 4]) # [1, 2, 3, 4]
C = torch.cat((A.view(1), B)) # [0, 1, 2, 3, 4]
2 Likes
7

A = torch.tensor(0)
B = torch.tensor([1,2,3])
C = torch.cat((A.reshape(1), B))

8

this works best for me. thanks!

9

doesn’ work on gpu though… what would you suggest to use the tensor on the gpu?

10

This doesn’t work anymore in the latest pytorch :frowning: any alternative? thanks

11

If you do torch.empty(10,0), then you can concatenate it to torch.rand(10,24)

12

Thanks I’ll try that

14

@Giorgio It should work with torch.cat((torch.zeros(0, 3), torch.zeros(3, 3))) All the other dimension except the concatenation dimension should be same, and as you can see torch.zeros(0, 3) and torch.zeros(0, 0) are same