How to Reverse Order of Rows in a Tensor-CodePudding

I'm trying to reverse the order of the rows in a tensor that I create. I have tried with tensorflow and pytorch. Only thing I have found is the torch.flip() method. This does not work as it reverses not only the order of the rows, but also all of the elements in each row. I want the elements to remain the same. Is there an array operation of this to index the integers? For instance:

 tensor_a = [1, 2, 3]
       [4, 5, 6]
       [7, 8, 9]

I want it to be returned as:
       [7, 8, 9]
       [4, 5, 6]
       [1, 2, 3]

 however, torch.flip(tensor_a) = 
       [9, 8, 7]
       [6, 5, 4]
       [3, 2, 1]

Anyone have any suggestions?

CodePudding user response：

According to documentation torch.flip has argument dims, which control what axis to be flipped. In this case torch.flip(tensor_a, dims=(0,)) will return expected result. Also torch.flip(tensor_a) will reverse all tensor, and torch.flip(tensor_a, dims=(1,)) will reverse every row, like [1, 2, 3] --> [3, 2, 1].

CodePudding user response：

You need to set axis to flip on it like below:

a = torch.arange(9).view(3,3)
# tensor([[0, 1, 2],
#         [3, 4, 5],
#         [6, 7, 8]])

torch.flip(a, [0])
# tensor([[6, 7, 8],
#         [3, 4, 5],
#         [0, 1, 2]])

torch.flip(a, [1])
# tensor([[2, 1, 0],
#         [5, 4, 3],
#         [8, 7, 6]])

torch.flip(a, [0,1])
# tensor([[8, 7, 6],
#         [5, 4, 3],
#         [2, 1, 0]])

As you can see you need torch.flip(a, [0])