html_url,issue_url,id,node_id,user,created_at,updated_at,author_association,body,reactions,performed_via_github_app,issue
https://github.com/pydata/xarray/issues/1408#issuecomment-919974416,https://api.github.com/repos/pydata/xarray/issues/1408,919974416,IC_kwDOAMm_X8421bIQ,4160723,2021-09-15T12:27:34Z,2021-09-15T12:27:34Z,MEMBER,"@fujiisoup the behavior that you expect has been implemented in #5692 (I still need to fix/update the tests):

```python
>>> ds.sel(x=2)
<xarray.Dataset>
Dimensions:  (y: 2)
Coordinates:
  * y        (y) <U1 'a' 'b'
    x        int64 2
Data variables:
    foo      (y) int64 2 5
```

```python
>>> ds.isel(yx=0)
<xarray.Dataset>
Dimensions:  ()
Coordinates:
    yx       object ('a', 1)
    y        <U1 'a'
    x        int64 1
Data variables:
    foo      int64 1
```

Note that for the latter example, the `yx` coordinate may eventually become irrelevant for multi-indexes (we'll need only the level coordinates).

@gabriel-abrahao feel free to open a new issue for your suggestion.
","{""total_count"": 3, ""+1"": 2, ""-1"": 0, ""laugh"": 0, ""hooray"": 1, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,228295383
https://github.com/pydata/xarray/issues/1408#issuecomment-301356080,https://api.github.com/repos/pydata/xarray/issues/1408,301356080,MDEyOklzc3VlQ29tbWVudDMwMTM1NjA4MA==,4160723,2017-05-15T01:34:15Z,2017-05-15T02:03:06Z,MEMBER,"(mmh apparently I forgot to post a 2nd comment I wrote)

 > I'm just wondering if it really makes sense to keep a MultiIndex for a coordinate that is not a dimension anymore like in this case.

And this is just a nonsense :) Sorry it is late!

Yep I agree it would be nice to have scalar coordinates in both cases.

","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,228295383
https://github.com/pydata/xarray/issues/1408#issuecomment-301351084,https://api.github.com/repos/pydata/xarray/issues/1408,301351084,MDEyOklzc3VlQ29tbWVudDMwMTM1MTA4NA==,4160723,2017-05-15T00:33:15Z,2017-05-15T00:33:15Z,MEMBER,"The current behavior is actually dictated by pandas and I think it was initially intentional (before we could access MultiIndex levels as virtual coordinates).

In the first example `MultiIndex.get_loc_level()` is called, which doesn't return a `MutliIndex`:

```python
In [11]: mdix = ds.yx.to_index()

In [12]: midx.get_loc_level(2, level='x')
Out[12]: 
(array([False,  True, False, False,  True, False], dtype=bool),
 Index(['a', 'b'], dtype='object', name='y'))
```

If we want to keep the `MultiIndex` in this case, then I think we can just ignore `new_indexes` returned by `indexing.remap_label_indexers` and remove [Dataset._replace_indexes](https://github.com/pydata/xarray/blob/80ddad99dbee1197c93f61ef9048b83d9f29d00d/xarray/core/dataset.py#L578).

But we still have to choose whether automatically renaming the dimension makes sense or not, i.e., choose between

```python
In [5]: ds.sel(x=2)
Out[5]:
<xarray.Dataset>
Dimensions:  (yx: 2)
Coordinates:
  * yx       MultiIndex 
  - y        (yx) object 'a' 'b'
  - x        (yx) int64 2 2
Data variables:
    foo      (yx) int64 2 5
```

and 

```python
In [5]: ds.sel(x=2)
Out[5]:
<xarray.Dataset>
Dimensions:  (y: 2)
Coordinates:
  * y        (y) object 'a' 'b'
    x        (y) int64 2 2
Data variables:
    foo      (y) int64 2 5
```

---

The second issue is also due to how MultiIndex works in pandas:

```python
In [10]: midx[0]
Out[10]: ('a', 1)

In [11]: midx[[0, 1]]
Out[11]: 
MultiIndex(levels=[['a', 'b'], [1, 2, 3]],
           labels=[[0, 0], [0, 1]],
           names=['y', 'x'])
```

I'm just wondering if it really makes sense to keep a MultiIndex for a coordinate that is not a dimension anymore like in this case.
","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,228295383