issues: 324409064

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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
324409064 MDU6SXNzdWUzMjQ0MDkwNjQ= 2160 pandas-0.23 breaks stack with duplicated indices 6213168 closed 0     3 2018-05-18T13:23:26Z 2018-05-26T03:29:46Z 2018-05-26T03:29:46Z MEMBER      

In this script: ``` import pandas import xarray

df = pandas.DataFrame( [[1, 2], [3, 4]], index=['foo', 'foo'], columns=['bar', 'baz']) print(df.stack())

a = xarray.DataArray(df) print(a.stack(s=a.dims)) ```

The first part works both with pandas 0.22 and 0.23. The second part works in xarray 0.10. 4 + pandas 0.22, and crashes with pandas 0.23:

File "/mnt/resource/tmp/anaconda_guido/lib/python3.6/site-packages/xarray/core/dataarray.py", line 1115, in stack ds = self._to_temp_dataset().stack(**dimensions) File "/mnt/resource/tmp/anaconda_guido/lib/python3.6/site-packages/xarray/core/dataset.py", line 2123, in stack result = result._stack_once(dims, new_dim) File "/mnt/resource/tmp/anaconda_guido/lib/python3.6/site-packages/xarray/core/dataset.py", line 2092, in _stack_once idx = utils.multiindex_from_product_levels(levels, names=dims) File "/mnt/resource/tmp/anaconda_guido/lib/python3.6/site-packages/xarray/core/utils.py", line 96, in multiindex_from_product_levels return pd.MultiIndex(levels, labels, sortorder=0, names=names) File "/mnt/resource/tmp/anaconda_guido/lib/python3.6/site-packages/pandas/core/indexes/multi.py", line 240, in __new__ result._verify_integrity() File "/mnt/resource/tmp/anaconda_guido/lib/python3.6/site-packages/pandas/core/indexes/multi.py", line 283, in _verify_integrity level=i)) ValueError: Level values must be unique: ['foo', 'foo'] on level 0

 
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   completed 13221727 issue

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