Index Multidimensional Torch Tensor By Another Multidimensional Tensor

I have a tensor x in pytorch let's say of shape (5,3,2,6) and another tensor idx of shape (5,3,2,1) which contain indices for every element in first tensor. I want a slicing of the

Solution 1:

From what I understand from the comments, you need idx to be index in the last dimension and each index in idx corresponds to similar index in x (except for the last dimension). In that case (this is the numpy version, you can convert it to torch):

ind = np.indices(idx.shape)
ind[-1] = idx
x[tuple(ind)]

output:

[[10]
 [43]]

Solution 2:

You can use range; and squeeze to get proper idx dimension like

x[range(x.size(0)), idx.squeeze()]tensor([10., 43.])

# or
x[range(x.size(0)), idx.squeeze()].unsqueeze(1)
tensor([[10.],
        [43.]])

Solution 3:

Here's the one that works in PyTorch using gather. The idx needs to be in torch.int64 format which the following line will ensure (note the lowercase of 't' in tensor).

idx = torch.tensor([[0],
                    [2]])
torch.gather(x, 1, idx) # 1 is the axis to index here
tensor([[10.],
        [43.]])