issues: 189721898

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id node_id number title user state locked assignee milestone comments created_at updated_at closed_at author_association active_lock_reason draft pull_request body reactions performed_via_github_app state_reason repo type
189721898 MDU6SXNzdWUxODk3MjE4OTg= 1126 unstack raises error when there is only one dimension stacked 14000880 closed 0     3 2016-11-16T14:34:05Z 2019-01-25T06:43:01Z 2019-01-25T06:43:01Z NONE      

I am aware that stack()/unstack() is meant to be used for combining/splitting multiple dimensions. Still, I wonder if it should throw an error when used on a dataset with only one dimension:

ds = xr.Dataset() ds['var'] = xr.DataArray(np.array([3., 4.]), dims=('dim1')) ds_s = ds.stack(z=['dim1']) ds_s.unstack('z') ValueError: cannot unstack a dimension that does not have a MultiIndex

I stumbled upon this when implementing a stack-groupby-apply-unstack pattern on a dataset which normally has more than one dimension to stack, but sometimes might contain only one. I can circumvent this quite easily by checking if there is only one dimension to stack and not using stack/unstack then, but I somehow expected it to work without treating this case in a special way. 

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