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/1603#issuecomment-442809859,https://api.github.com/repos/pydata/xarray/issues/1603,442809859,MDEyOklzc3VlQ29tbWVudDQ0MjgwOTg1OQ==,6815844,2018-11-29T12:05:03Z,2018-11-29T12:05:03Z,MEMBER,"I am late for the party (but still only have time to write a short comment).
I am a big fan of MultiIndex and like @shoyer 's idea.
`ds.sel(multi=list_of_pairs)` can probably be replaced by `ds.sel(x=..., y=...)`, but how about `reindex` along MultiIndex?
I have encountered its use cases several times.
I also think it would be nice to have MultiIndex as a variable.","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,262642978
https://github.com/pydata/xarray/issues/1603#issuecomment-379920389,https://api.github.com/repos/pydata/xarray/issues/1603,379920389,MDEyOklzc3VlQ29tbWVudDM3OTkyMDM4OQ==,6815844,2018-04-09T23:03:03Z,2018-04-09T23:04:01Z,MEMBER,"@shoyer, thank you for detailing.
I am thinking how can we establish the following `selecting-concatenating` behavior with MultiIndex(-like) coordinate with our new Indexes machinary,
```
xr.concat([da.isel(x=i) for i in range(len(da['x':))], dim='x')
```
Personally, I think it would be nice if we could recover the original Index structue.
We may need to track Indexes object even when the corresponding dimension becomes one dimensional?
But scalar index sounds strange...
Or, we may give up to restore the original coordinate structure during the above action, but stil keep them as ordinary coodinates.","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,262642978
https://github.com/pydata/xarray/issues/1603#issuecomment-336381864,https://api.github.com/repos/pydata/xarray/issues/1603,336381864,MDEyOklzc3VlQ29tbWVudDMzNjM4MTg2NA==,6815844,2017-10-13T08:09:25Z,2017-10-13T08:09:25Z,MEMBER,"Thanks for the details.
(Sorry for my late responce. It took a long for me to understand what does it look like.)
I am wondering what the advantageous cases which are realized with this `Index` concept are.
As far as my understanding is correct,
1. It will enable more flexible indexing, e.g. more than one Indexes are associated with one dimension and we can select from these coordinate values very flexibly.
2. It will naturally integrate more advanced Indexes such as `KDTree`
Are they correct?
> Probably the most elegant rule would again be to check all indexed variables for exact matches.
That sounds reasonable.
> In principle, this data model would allow for two mostly equivalent indexing schemes: MultiIndex[time, space] vs two indexes Index[time] and Index[space].
I like the latter one, as it is easier to understand even for non-pandas users.
What does the actual implementation look like?
`xr.Dataset.indexes` will be an `OrderedDict` that maps from variable's name to its associated dimension?
Actual instance of Index will be one of `xr.Dataset.variables`?","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,262642978
https://github.com/pydata/xarray/issues/1603#issuecomment-334125888,https://api.github.com/repos/pydata/xarray/issues/1603,334125888,MDEyOklzc3VlQ29tbWVudDMzNDEyNTg4OA==,6815844,2017-10-04T11:25:14Z,2017-10-04T12:43:59Z,MEMBER,"@shoyer, could you add more details of this idea?
I think I do not yet fully understand the practical difference between `dim` and `index`.
1. Use cases of the independent `Index` and `dims`
Would it be general cases where `dimension` and `index` are independent?
(It is the case only for `MultiIndex` and `KDtree`)?
2. `MultiIndex` implementation
In `MultiIndex` case, will a xarray object store a `MultiIndex` object and also the level variables as `Variable` objects (there will be some duplicates)?
If `indexes[dim]` returns multiple `Variable`s, which realizes a `MultiIndex`-like structure without `pd.MultiIndex`, `indexes` would be very different from `dim`,
because a single dimension can have multiple `indexes`.
","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,262642978
https://github.com/pydata/xarray/issues/1603#issuecomment-334043044,https://api.github.com/repos/pydata/xarray/issues/1603,334043044,MDEyOklzc3VlQ29tbWVudDMzNDA0MzA0NA==,6815844,2017-10-04T03:51:57Z,2017-10-04T03:51:57Z,MEMBER,"I think we currently assume `variables[dim]` is an Index.
Does your proposal means that `Dataset` will keep an additional attribute `indexes`, and `indexes[dim]` gives a `pd.Index` (or `pd.MultiIndex`, `KDTree`)?
It sounds a much cleaner data model.","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,262642978
https://github.com/pydata/xarray/issues/1603#issuecomment-334029215,https://api.github.com/repos/pydata/xarray/issues/1603,334029215,MDEyOklzc3VlQ29tbWVudDMzNDAyOTIxNQ==,6815844,2017-10-04T01:55:02Z,2017-10-04T01:55:02Z,MEMBER,"I'm using `MultiIndex` a lot,
but I noticed that it is just a workaround to index along multiple kinds of coordinate.
Consider the following example,
```python
In [1]: import numpy as np
...: import xarray as xr
...: da = xr.DataArray(np.arange(5), dims=['x'],
...: coords={'experiment': ('x', [0, 0, 0, 1, 1]),
...: 'time': ('x', [0.0, 0.1, 0.2, 0.0, 0.15])})
...:
In [2]: da
Out[2]:
array([0, 1, 2, 3, 4])
Coordinates:
experiment (x) int64 0 0 0 1 1
time (x) float64 0.0 0.1 0.2 0.0 0.15
Dimensions without coordinates: x
```
I want to do something like this
```python
da.sel(experiment=0).sel(time=0.1)
```
but it cannot.
MultiIndexing enables this,
```python
In [2]: da = da.set_index(exp_time=['experiment', 'time'])
...: da
...:
Out[2]:
array([0, 1, 2, 3, 4])
Coordinates:
* exp_time (exp_time) MultiIndex
- experiment (exp_time) int64 0 0 0 1 1
- time (exp_time) float64 0.0 0.1 0.2 0.0 0.15
Dimensions without coordinates: x
```
If we could make a selection from a non-index coordinate,
`MultiIndex` is not necessary for this case.
I think there should be other important usecases of `MultiIndex`.
I would be happy if anyone could list them in this issue.
","{""total_count"": 2, ""+1"": 2, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,262642978