What I want to do is gathering elements from 10x20 tensor `x`

according to the class label tensor `y`

whose shape is (10,).

I couldn’t understand this error because I didn’t specify index 19 in dim 0.

Could anyone help me?

```
❯ ipython
Python 3.6.5 |Anaconda custom (64-bit)| (default, Apr 29 2018, 16:14:56)
Type 'copyright', 'credits' or 'license' for more information
IPython 6.5.0 -- An enhanced Interactive Python. Type '?' for help.
In [1]: import torch
In [2]: x = torch.empty(10, 20).uniform_().float(); y = torch.randint(0, 20, (10,)).long()
In [3]: indices = torch.stack((torch.arange(x.size(0)), y), 1)
In [4]: x[indices]
---------------------------------------------------------------------------
RuntimeError Traceback (most recent call last)
<ipython-input-4-a9c39fcc26e5> in <module>()
----> 1 x[indices]
RuntimeError: index 19 is out of bounds for dimension 0 with size 10
In [5]: indices
Out[5]:
tensor([[ 0, 18],
[ 1, 10],
[ 2, 4],
[ 3, 13],
[ 4, 7],
[ 5, 5],
[ 6, 0],
[ 7, 8],
[ 8, 19],
[ 9, 8]])
In [6]: torch.__version__
Out[6]: '1.0.0.dev20180921'
In [8]: x[9, 19]
Out[8]: tensor(0.8050) <- of course, this worked.
```