Modify the rows of a tensor at specific indices given by a list (Pytorch)

Question

I have a tensor X with shape (N,M) and a list of indices idx_list. I would like to modify X but only at the rows given by idx_list.
So I'd like to do something like this:

X[idx_list, :] = Y

Y is a tensor with shape (len(idx_list), M)

Noob ML Dude · Accepted Answer · 2022-10-18 13:02:04Z

1

The solution is mentioned in your question. The usual slicing notation that's used in numpy arrays works well with PyTorch tensors as well.

X[idx_list, :] = Y

Here's a screenshot from Jupyter notebook illustrating it:

Your approach posted as answer would work too

X[(torch.tensor(idx_list),)] = Y

However, you do not need to complicate it like this by converting the idx_list into a tensor. Slicing is preferably done using standard Python lists.

edited Oct 18, 2022 at 13:02

answered Oct 18, 2022 at 12:25

Noob ML Dude

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1 Comment

SuperTardigrade Over a year ago

Very clear, thanks a lot!

SuperTardigrade · Accepted Answer · 2022-10-18 10:14:55Z

0

This works pretty well:

X[(torch.tensor(idx_list),)] = Y

answered Oct 18, 2022 at 10:14

SuperTardigrade

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