issues: 1889195671

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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
1889195671 I_kwDOAMm_X85wmtaX 8166 Dataset.from_dataframe: deprecate expanding the multi-index 4160723 open 0     3 2023-09-10T15:54:31Z 2023-09-11T06:20:50Z   MEMBER      

What is your issue?

Let's continue here the discussion about changing the behavior of Dataset.from_dataframe (see https://github.com/pydata/xarray/pull/8140#issuecomment-1712485626).

The current behaviour of Dataset.from_dataframe where it always unstacks feels wrong to me. To me, it seems sensible that Dataset.from_dataframe(df) automatically creates a Dataset with PandasMultiIndex if df has a MultiIndex. The user can then use that or quite easily unstack to a dense or sparse array.

If we don't unstack anymore the multi-index in Dataset.from_dataframe, are we OK that the "Dataset -> DataFrame -> Dataset" round-trip will not yield expected results unless we unstack explicitly?

```python ds = xr.Dataset( {"foo": (("x", "y"), [[1, 2], [3, 4]])}, coords={"x": ["a", "b"], "y": [1, 2]}, )

df = ds.to_dataframe() ds2 = xr.Dataset.from_dataframe(df, dim="z")

ds2.identical(ds) # False

ds2.unstack("z").identical(ds) # True ```

cc @max-sixty @dcherian 

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