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/2375#issuecomment-415201313,https://api.github.com/repos/pydata/xarray/issues/2375,415201313,MDEyOklzc3VlQ29tbWVudDQxNTIwMTMxMw==,6815844,2018-08-22T22:22:48Z,2018-08-22T22:22:48Z,MEMBER,"> But maybe it is better to choose the first dim that is MultiIndex rather than the first dim.

*first* dimension is not well defined in `Dataset`, as it is a union of the dims of all the dataarrays it has.
For example, in the following example, `ds.unstack()['var']` and `da['var'].unstack()` will give different results.

```python
In [15]: import numpy as np
    ...: import xarray as xr
    ...: 
    ...: ds = xr.Dataset({'var': (('x', 'y', 'z', 'w'), np.random.randn(2,3,4,5))})
    ...: ds = ds.stack(b=['z', 'w']).stack(a=['x', 'y'])
    ...: ds
    ...: 
Out[15]: 
<xarray.Dataset>
Dimensions:  (a: 6, b: 20)
Coordinates:
  * b        (b) MultiIndex
  - z        (b) int64 0 0 0 0 0 1 1 1 1 1 2 2 2 2 2 3 3 3 3 3
  - w        (b) int64 0 1 2 3 4 0 1 2 3 4 0 1 2 3 4 0 1 2 3 4
  * a        (a) MultiIndex
  - x        (a) int64 0 0 0 1 1 1
  - y        (a) int64 0 1 2 0 1 2
Data variables:
    var      (b, a) float64 -1.277 -0.4031 -0.3816 ... 1.398 0.6763 -0.6735

In [16]: list(ds.dims)
Out[16]: ['a', 'b']

In [17]: list(ds['var'].dims)
Out[17]: ['b', 'a']
```

> but in that case should we allow passing in multiple dims? 

I like this direction.
`stack` accepts multiple pairs of dimensions to be stacked, like `ds.stack(a=['x', 'y'], b=['z', 'w'])`.
In this method, it repeatedly calls `_stack_once` method.
I think `unstack` also can have the similar logic.


","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,352677925
https://github.com/pydata/xarray/pull/2375#issuecomment-414860789,https://api.github.com/repos/pydata/xarray/issues/2375,414860789,MDEyOklzc3VlQ29tbWVudDQxNDg2MDc4OQ==,6815844,2018-08-22T00:01:45Z,2018-08-22T00:01:45Z,MEMBER,"Thanks, @jsignell.

I like this idea (`unstack` without explicit dimension names), but I think we may need to decide what API would be the best.
My particular concern is 
+ what should be done if DataArray or Dataset has multiple MultiIndexes.
  Maybe do we unstack all the MultiIndexes?
+ we have similar method `reset_index`. Do we also want to make `dim` optional?

For `unstack_like`, I'm not sure it is worth adding as a top level function as `xr.full_like(other, data).unstack()` is simple enoguh...","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,352677925