issue_comments: 391919607

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https://github.com/pydata/xarray/issues/2180#issuecomment-391919607 https://api.github.com/repos/pydata/xarray/issues/2180 391919607 MDEyOklzc3VlQ29tbWVudDM5MTkxOTYwNw== 6815844 2018-05-25T02:06:47Z 2018-05-25T02:19:45Z MEMBER

For referene the original issue in #2068 was ```python In [4]: ds = xr.Dataset() ...: ds.coords['source'] = (['a', 'b', 'c'], np.random.random((2, 3, 4))) ...: ds.coords['unrelated'] = (['a', 'c'], np.random.random((2, 4))) ...: ds ...: Out[4]: <xarray.Dataset> Dimensions: (a: 2, b: 3, c: 4) Coordinates: source (a, b, c) float64 0.4158 0.07152 0.4258 0.4382 0.6616 0.142 ... unrelated (a, c) float64 0.9318 0.03723 0.4226 0.9472 0.8753 0.7022 ... Dimensions without coordinates: a, b, c Data variables: empty

In [5]: ds['dest-2'] = xr.ones_like(ds['source'].isel(c=0)) ...: ds ...: Out[5]: <xarray.Dataset> Dimensions: (a: 2, b: 3) Coordinates: source (a, b) float64 0.4158 0.6616 0.1583 0.7821 0.221 0.2555 unrelated (a) float64 0.9318 0.8753 Dimensions without coordinates: a, b Data variables: dest-2 (a, b) float64 1.0 1.0 1.0 1.0 1.0 1.0 `` whereds['unrelated']drops dimensionc`. We changed this behavior in #2087, but I think it was a wrong direction.

The previous behavior might be OK as long as unrelated is a coordinate variable.

EDIT: I still feel something strange both in the previous and current behavior of __setitem__ with coord. Generally, as @crusaderky has pointed out, the right join will be a better choice. But In the above example, dropping the dimension of c of 'unrelated' looks also awkward.

 
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