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/pull/1412#issuecomment-302883780,https://api.github.com/repos/pydata/xarray/issues/1412,302883780,MDEyOklzc3VlQ29tbWVudDMwMjg4Mzc4MA==,4160723,2017-05-20T16:31:43Z,2017-05-20T16:31:43Z,MEMBER,"I also agree that a MultiIndex wrapper would be to be the way to go. I think I understand the diagrams, but what remains a bit unclear to me is how this could be implemented.

In particular, how would this wrapper work with `IndexVariable`?

Currently, `IndexVariable` warps either a `pandas.Index` or a `pandas.MultiIndex` and for the latter case `IndexVariable.get_level_variable` can generate new `IndexVariable` objects so that MultiIndex levels are accessible as ""virtual coordinates"".

Would `IndexVariable` warp a MultiIndex wrapper instead (levels + scalars), and also be able to generate new scalar `Variable` objects that will be accessible as virtual coordinates?

This is maybe slightly off topic, but more generally I'm also wondering how this would co-exist with potentially other kinds of multi-level indexes (see this [comment](https://github.com/pydata/xarray/issues/475#issuecomment-241821366)).




","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,229370997
https://github.com/pydata/xarray/pull/1412#issuecomment-302358284,https://api.github.com/repos/pydata/xarray/issues/1412,302358284,MDEyOklzc3VlQ29tbWVudDMwMjM1ODI4NA==,4160723,2017-05-18T09:56:28Z,2017-05-18T09:58:06Z,MEMBER,"A possible direction to reduce the `if` statements in many different places would be to just return `pos_indexers` in `indexing.remap_level_indexers` - as it was the case before adding multi-index support - and instead put in  `Dataset.isel` all the logic for checking `MultiIndex` and maybe convert it to `Index` and/or scalar coordinates and maybe rename dimension.

This would simplify many things, although I haven't thought about about all other possible issues it would create (perfomance, etc.). Also, `DataArray.loc` doesn't seem to use `Dataset.isel`.

Here is another case related to this PR. From the example in the linked issue, the current behavior is

```python
In [9]: ds.isel(yx=[0, 1])
Out[9]: 
<xarray.Dataset>
Dimensions:  (yx: 2)
Coordinates:
  * yx       (yx) MultiIndex
  - y        (yx) object 'a' 'a'
  - x        (yx) int64 1 2
Data variables:
    foo      (yx) int64 1 2
```

Do we want to also change the behavior to this?

```python
In [10]: ds.isel(yx=[0, 1])
Out[10]: 
<xarray.Dataset>
Dimensions:  (x: 2)
Coordinates:
  * x        (x) int64 1 2
    y        object 'a'
Data variables:
    foo      (x) int64 1 2
```

To me it looks like it is a bit too magical, but just wondering what you think... 
","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,229370997