issue_comments: 448887168

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https://github.com/pydata/xarray/pull/2621#issuecomment-448887168 https://api.github.com/repos/pydata/xarray/issues/2621 448887168 MDEyOklzc3VlQ29tbWVudDQ0ODg4NzE2OA== 6815844 2018-12-20T06:22:38Z 2018-12-20T06:22:38Z MEMBER

@shoyer

My inclination was just to copy what pandas does (which is only removing unused levels in unstack)

Thanks. I will take a look the source later.

Can you explain why matters for .sel()?

Selection of non-exsiting level variable should be KeyError, but it gives a 0-size index.

```python In [8]: ds = xr.DataArray(np.arange(40).reshape(8, 5), dims=['x', 'y'],
coords={'x': np.arange(8), 'y': np.arange(5)}).stack(xy=['x', 'y'])

In [9]: ds.isel(xy=ds['x'] < 4).sel(x=5) # should be KeyError Out[9]: <xarray.DataArray (y: 0)> array([], dtype=int64) Coordinates: * y (y) int64 ```

 
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