解析Pytorch中的torch.gather()函数

input=torch.tensor([[1,2,3],[4,5,6]]) #作为输入
 
index1=torch.tensor([[0,1,1],[0,1,1]]) #作为索引矩阵
 
# dim=0时,按列进行索引
print (torch.gather(input,dim=0,index=index1))
 
# dim=1时,按行进行索引
print (torch.gather(input,dim=1,index=index1))

# 按列进行索引
tensor([[1, 5, 6],
  [4, 2, 6]])
 
# 按行进行索引
tensor([[1, 2, 2],
  [5, 4, 5]])

def gather(self, input, dim, index, *args, **kwargs): 
  
  For a 3-D tensor the output is specified by::
  
out[i][j][k] = input[index[i][j][k]][j][k]  # if dim == 0
out[i][j][k] = input[i][index[i][j][k]][k]  # if dim == 1
out[i][j][k] = input[i][j][index[i][j][k]]  # if dim == 2  
 
  Args:
input (Tensor): the source tensor
dim (int): the axis along which to index
index (LongTensor): the indices of elements to gather  

  Example::
  
>>> t = torch.tensor([[1, 2], [3, 4]])
>>> torch.gather(t, 1, torch.tensor([[0, 0], [1, 0]]))
tensor([[ 1,  1],
  [ 4,  3]])