issue_comments: 302170558

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https://github.com/pydata/xarray/pull/1412#issuecomment-302170558 https://api.github.com/repos/pydata/xarray/issues/1412 302170558 MDEyOklzc3VlQ29tbWVudDMwMjE3MDU1OA== 1217238 2017-05-17T17:42:58Z 2017-05-17T17:42:58Z MEMBER

variable.getitem now returns an OrderedDict if a single element is selected from MultiIndex.

I don't like this change. It breaks an important invariant, which is that indexing a Variable returns another Variable.

I do agree with indexing along a MultiIndex dimension should unpacking the tuple for coordinates, but only for coordinates. So this needs to be somewhere in the Dataset.isel logic, not Variable.isel.

Consider indexing ds['yx'] from your example in the linked issue. With the current version of xarray: ``` In [7]: ds['yx'] Out[7]: <xarray.DataArray 'yx' (yx: 6)> array([('a', 1), ('a', 2), ('a', 3), ('b', 1), ('b', 2), ('b', 3)], dtype=object) Coordinates: * yx (yx) MultiIndex - y (yx) object 'a' 'a' 'a' 'b' 'b' 'b' - x (yx) int64 1 2 3 1 2 3

In [8]: ds['yx'][0] Out[8]: <xarray.DataArray 'yx' ()> array(('a', 1), dtype=object) Coordinates: yx object ('a', 1) We want to change the indexing behavior to this: In [8]: ds['yx'][0] Out[8]: <xarray.DataArray 'yx' ()> array(('a', 1), dtype=object) Coordinates: y object 'a' x int64 1 ``` But we don't want to change what happens to the DataArray itself -- it should still be a scalar object array.

I tested this example on your PR branch, and it actually crashes with KeyError.

 
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