html_url,issue_url,id,node_id,user,created_at,updated_at,author_association,body,reactions,performed_via_github_app,issue
https://github.com/pydata/xarray/issues/6610#issuecomment-1128588208,https://api.github.com/repos/pydata/xarray/issues/6610,1128588208,IC_kwDOAMm_X85DROOw,22245117,2022-05-17T08:40:04Z,2022-05-17T15:04:04Z,CONTRIBUTOR,"I'm getting errors with multi-indexes and `flox`. Is this expected and related to this issue, or should I open a separate issue?

```python
import numpy as np

import xarray as xr

ds = xr.Dataset(
    dict(a=((""z"",), np.ones(10))),
    coords=dict(b=((""z""), np.arange(2).repeat(5)), c=((""z""), np.arange(5).repeat(2))),
).set_index(bc=[""b"", ""c""])
grouped = ds.groupby(""bc"")

with xr.set_options(use_flox=False):
    grouped.sum()  # OK

with xr.set_options(use_flox=True):
    grouped.sum()  # Error
```
```
Traceback (most recent call last):
  File ""/Users/mattia/MyGit/test.py"", line 15, in <module>
    grouped.sum()
  File ""/Users/mattia/MyGit/xarray/xarray/core/_reductions.py"", line 2763, in sum
    return self._flox_reduce(
  File ""/Users/mattia/MyGit/xarray/xarray/core/groupby.py"", line 661, in _flox_reduce
    result = xarray_reduce(
  File ""/Users/mattia/mambaforge/envs/sarsen_dev/lib/python3.10/site-packages/flox/xarray.py"", line 373, in xarray_reduce
    actual[k] = v.expand_dims(missing_group_dims)
  File ""/Users/mattia/MyGit/xarray/xarray/core/dataset.py"", line 1427, in __setitem__
    self.update({key: value})
  File ""/Users/mattia/MyGit/xarray/xarray/core/dataset.py"", line 4432, in update
    merge_result = dataset_update_method(self, other)
  File ""/Users/mattia/MyGit/xarray/xarray/core/merge.py"", line 1070, in dataset_update_method
    return merge_core(
  File ""/Users/mattia/MyGit/xarray/xarray/core/merge.py"", line 722, in merge_core
    aligned = deep_align(
  File ""/Users/mattia/MyGit/xarray/xarray/core/alignment.py"", line 824, in deep_align
    aligned = align(
  File ""/Users/mattia/MyGit/xarray/xarray/core/alignment.py"", line 761, in align
    aligner.align()
  File ""/Users/mattia/MyGit/xarray/xarray/core/alignment.py"", line 550, in align
    self.assert_unindexed_dim_sizes_equal()
  File ""/Users/mattia/MyGit/xarray/xarray/core/alignment.py"", line 450, in assert_unindexed_dim_sizes_equal
    raise ValueError(
ValueError: cannot reindex or align along dimension 'bc' because of conflicting dimension sizes: {10, 6} (note: an index is found along that dimension with size=10)
```","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,1236174701