b = torch.Tensor([[1,2,3],[4,5,6]])
print b
index_1 = torch.LongTensor([[0,1],[2,0]])
index_2 = torch.LongTensor([[0,1,1],[0,0,0]])
print torch.gather(b, dim=1, index=index_1)
print torch.gather(b, dim=0, index=index_2)

 1 2 3
 4 5 6
[torch.FloatTensor of size 2x3]


 1 2
 6 4
[torch.FloatTensor of size 2x2]


 1 5 6
 1 2 3
[torch.FloatTensor of size 2x3]

torch.gather(input, dim, index, out=None) → Tensor

 Gathers values along an axis specified by dim.

 For a 3-D tensor the output is specified by:

 out[i][j][k] = input[index[i][j][k]][j][k] # dim=0
 out[i][j][k] = input[i][index[i][j][k]][k] # dim=1
 out[i][j][k] = input[i][j][index[i][j][k]] # dim=2

 Parameters: 

  input (Tensor) – The source tensor
  dim (int) – The axis along which to index
  index (LongTensor) – The indices of elements to gather
  out (Tensor, optional) – Destination tensor

 Example:

 > t = torch.Tensor([[1,2],[3,4]])
 > torch.gather(t, 1, torch.LongTensor([[0,0],[1,0]]))
  1 1
  4 3
 [torch.FloatTensor of size 2x2]