pytorch tensor change dimensionallity to count adjacent values

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My objective it to count all adjacent unique values of a tensor x.
Say my tensor is (x looks like a list but it is a pytorch tensor)

x = [1,2,1,2,4,5]

I would want my output to be:

[1,2] = 2
[2,1] = 1
[2,4] = 1
[4,5] = 1

I thought about changing the dimensionality of the tensor to look like:

x = [[1,2],[2,1],[1,2],[2,4],[4,5]]

using tensor.view but couldn't find a solution that works for a tensor of any length. Any ideas if this is even the best way to go about this? is there some built-in function?

tensor pytorch python
1 Answers

As @ihdv showed, you can stack shifted views of x with torch.stack or torch.vstack in order to get a tensor of pairs with overlapping windows.

>>> p = torch.vstack((x[:-1], x[1:]))
tensor([[1., 2., 1., 2., 4.],
        [2., 1., 2., 4., 5.]])

Then you can apply torch.unique on it to get the statistics:

>>> p.unique(dim=1, return_counts=True)
(tensor([[1., 2., 2., 4.],
         [2., 1., 4., 5.]]), tensor([2, 1, 1, 1]))
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