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-729306620,https://api.github.com/repos/pydata/xarray/issues/1408,729306620,MDEyOklzc3VlQ29tbWVudDcyOTMwNjYyMA==,30908904,2020-11-18T00:56:45Z,2020-11-18T00:56:45Z,CONTRIBUTOR,"As a related issue, we could use an option for .sel to keep the selected variable as a singleton coordinate (an array of shape (1,)) instead of making it a scalar. ","{""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-695364856,https://api.github.com/repos/pydata/xarray/issues/1408,695364856,MDEyOklzc3VlQ29tbWVudDY5NTM2NDg1Ng==,26384082,2020-09-19T23:01:48Z,2020-09-19T23:01:48Z,NONE,"In order to maintain a list of currently relevant issues, we mark issues as stale after a period of inactivity

If this issue remains relevant, please comment here or remove the `stale` label; otherwise it will be marked as closed automatically
","{""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-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-301353831,https://api.github.com/repos/pydata/xarray/issues/1408,301353831,MDEyOklzc3VlQ29tbWVudDMwMTM1MzgzMQ==,6815844,2017-05-15T01:10:25Z,2017-05-15T01:10:25Z,MEMBER,"@benbovy Thanks for the comment.

Actually, I expected the following behavior
```python
In [1]: ds.sel(x=2)
Out[1]: 
<xarray.Dataset>
Dimensions:  (y: 2)
Coordinates:
  * y        (y) object 'a' 'b'
    x        int64 2
Data variables:
    foo      (y) int64 2 5
```
where the selected `x` is automatically converted to a scalar coordinate.

And also for the second issue, I expected something like
```python
In [2]: ds.isel(yx=0)
Out[2]: 
<xarray.Dataset>
Dimensions:  ()
Coordinates:
    y        <U1 'a'
    x        int64 1
Data variables:
    foo      int64 1
```
both `x` and `y` become scalar coordinates.

Back to the first issue, I personally prefer to the automatic renaming
because it enables the following chain methods,
```python
ds.sel(x=2).isel(y=1)
```
that might be intuitive especially for the hierarchic dimension structure.

","{""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
https://github.com/pydata/xarray/issues/1408#issuecomment-301303055,https://api.github.com/repos/pydata/xarray/issues/1408,301303055,MDEyOklzc3VlQ29tbWVudDMwMTMwMzA1NQ==,6815844,2017-05-14T10:19:15Z,2017-05-14T10:19:15Z,MEMBER,"@shoyer Thanks for the information.
(Sorry for my inaccurate ipython output)

Another related issue is 

```python
In[3]: ds.isel(yx=1)
Out[3]: 
<xarray.Dataset>
Dimensions:  ()
Coordinates:
    yx       object ('a', 1)
Data variables:
    foo      int64 1
```
where MultiIndex structure is totally gone.
(`ds.isel(yx=[0, 1])` works perfectly.)

I am now looking into the code. Do you guys have any idea to fix them?
I am thinking to modify [Index.remap_label_indexers](https://github.com/pydata/xarray/blob/master/xarray/core/indexing.py#L266)
so that it also returns `selected_dims` containing names of dims that should be converted to scalar coordinates.
","{""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-301218692,https://api.github.com/repos/pydata/xarray/issues/1408,301218692,MDEyOklzc3VlQ29tbWVudDMwMTIxODY5Mg==,1217238,2017-05-13T02:02:38Z,2017-05-13T02:02:38Z,MEMBER,"No, I don't think this was intentional/desired, though it might be slightly tricky to fix this with the current code structure.

@benbovy any thoughts?

For reference:
```python
In [4]: ds
Out[4]:
<xarray.Dataset>
Dimensions:  (yx: 6)
Coordinates:
  * yx       (yx) MultiIndex
  - y        (yx) object 'a' 'a' 'a' 'b' 'b' 'b'
  - x        (yx) int64 1 2 3 1 2 3
Data variables:
    foo      (yx) int64 1 2 3 4 5 6

In [5]: ds.sel(x=2)
Out[5]:
<xarray.Dataset>
Dimensions:  (y: 2)
Coordinates:
  * y        (y) object 'a' 'b'
Data variables:
    foo      (y) int64 2 5
```","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,228295383