Solved by SimonW in post #4 
              
              
                no… index_add_ is exactly what you need. why do you do ones_like(values)? can you look at the docs before complaining? 
>>> x = torch.zeros(5)
>>> x.index_add_(0, torch.tensor([0, 0, 4, 1]), torch.ones(4))
tensor([2., 1., 0., 0., 1.])