Hi,
I think this thread can help you with this:

  
    
    
    Set value of torch tensor up to some index nlp
  
  
    Hi, 
You can do this by creating binary mask. 
First we create a matrix with same shape as X filled with zeros, then put 1s where index matches with ind tensor and finally by using cumsum, set 1 after previously located points. Finally, we can mask X: 
X = torch.tensor(
    [[1,0,4,5,6],
     [3,6,7,10, 13],
     [1,4,2,8,21]])


ind = torch.tensor([2,3, 1])


mask = torch.zeros_like(X)
mask[(torch.arange(X.shape[0]), ind)] = 1
mask = 1 - mask.cumsum(dim=-1)
mask
# mask
# tensor([[1, 1, 0, 0, 0]…
  


But I have not tested it on large tensors.
Bests