title: Select tensor slice along a dimension based on index
body: <p>I have a PyTorch tensor of the following shape: (100, 5, 100). I need to convert it into a tensor of shape (100, 100) by selecting from each row only one item in the second dimension, meaning that of those 5 elements I only need one, with its corresponding 100 elements.</p>
  <p>To do this operation I have a second tensor of shape (100,) with the indices that specify which of those 5 items should be selected in each row.</p>
  <p>Is there a simple way to perform this selection without having to mess with the dimensions too much?</p>