Pytorch: How Can I Find Indices Of First Nonzero Element In Each Row Of A 2d Tensor?

I have a 2D tensor with some nonzero element in each row like this: import torch tmp = torch.tensor([[0, 0, 1, 0, 1, 0, 0], [0, 0, 0, 1, 1, 0, 0]], dtype=torch.

Solution 1:

I have simplified Iman's approach to do the following:

idx = torch.arange(tmp.shape[1], 0, -1)
tmp2= tmp * idx
indices = torch.argmax(tmp2, 1, keepdim=True)

Solution 2:

I could find a tricky answer for my question:

  tmp = torch.tensor([[0, 0, 1, 0, 1, 0, 0],
                     [0, 0, 0, 1, 1, 0, 0]], dtype=torch.float)
  idx = reversed(torch.Tensor(range(1,8)))
  print(idx)

  tmp2= torch.einsum("ab,b->ab", (tmp, idx))

  print(tmp2)

  indices = torch.argmax(tmp2, 1, keepdim=True)
  print(indeces)

The result is:

tensor([7., 6., 5., 4., 3., 2., 1.])
tensor([[0., 0., 5., 0., 3., 0., 0.],
       [0., 0., 0., 4., 3., 0., 0.]])
tensor([[2],
        [3]])

Solution 3:

All the nonzero values are equal, so argmax returns the first index.

tmp = torch.tensor([[0, 0, 1, 0, 1, 0, 0],
                    [0, 0, 0, 1, 1, 0, 0]])
indices = tmp.argmax(1)