Alignment of dataset with MultiIndex fails after applying xr.concat

[FabianHofmann]

What happened?

After applying the concat function to a dataset with a Multiindex, a lot of functions related to indexing are broken. For example, it is not possible to apply reindex_like to itself anymore.

The error is raised in the alignment module. It seems that the function find_matching_indexes does not find indexes that belong to the same dimension.

What did you expect to happen?

I expected the alignment to be functional and that these basic functions work.

Minimal Complete Verifiable Example

import xarray as xr
import pandas as pd

index = pd.MultiIndex.from_product([[1,2], ['a', 'b']], names=('level1', 'level2'))
index.name = 'dim'

var = xr.DataArray(1, coords=[index])
ds = xr.Dataset({"var":var})

new = xr.concat([ds], dim='newdim')
xr.Dataset(new) # breaks
new.reindex_like(new) # breaks

MVCE confirmation

• Minimal example — the example is as focused as reasonably possible to demonstrate the underlying issue in xarray.
• Complete example — the example is self-contained, including all data and the text of any traceback.
• Verifiable example — the example copy & pastes into an IPython prompt or Binder notebook, returning the result.
• New issue — a search of GitHub Issues suggests this is not a duplicate.

Relevant log output

Traceback (most recent call last):

  File "/tmp/ipykernel_407170/4030736219.py", line 11, in <cell line: 11>
    xr.Dataset(new) # breaks

  File "/home/fabian/.miniconda3/lib/python3.10/site-packages/xarray/core/dataset.py", line 599, in __init__
    variables, coord_names, dims, indexes, _ = merge_data_and_coords(

  File "/home/fabian/.miniconda3/lib/python3.10/site-packages/xarray/core/merge.py", line 575, in merge_data_and_coords
    return merge_core(

  File "/home/fabian/.miniconda3/lib/python3.10/site-packages/xarray/core/merge.py", line 752, in merge_core
    aligned = deep_align(

  File "/home/fabian/.miniconda3/lib/python3.10/site-packages/xarray/core/alignment.py", line 827, in deep_align
    aligned = align(

  File "/home/fabian/.miniconda3/lib/python3.10/site-packages/xarray/core/alignment.py", line 764, in align
    aligner.align()

  File "/home/fabian/.miniconda3/lib/python3.10/site-packages/xarray/core/alignment.py", line 550, in align
    self.assert_no_index_conflict()

  File "/home/fabian/.miniconda3/lib/python3.10/site-packages/xarray/core/alignment.py", line 319, in assert_no_index_conflict
    raise ValueError(

ValueError: cannot re-index or align objects with conflicting indexes found for the following dimensions: 'dim' (2 conflicting indexes)
Conflicting indexes may occur when
- they relate to different sets of coordinate and/or dimension names
- they don't have the same type
- they may be used to reindex data along common dimensions

Anything else we need to know?

No response

Environment

INSTALLED VERSIONS

commit: None
python: 3.10.5 | packaged by conda-forge | (main, Jun 14 2022, 07:04:59) [GCC 10.3.0]
python-bits: 64
OS: Linux
OS-release: 5.15.0-41-generic
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8
LOCALE: ('en_US', 'UTF-8')
libhdf5: 1.12.1
libnetcdf: 4.8.1

xarray: 2022.6.0
pandas: 1.4.2
numpy: 1.21.6
scipy: 1.8.1
netCDF4: 1.6.0
pydap: None
h5netcdf: None
h5py: 3.6.0
Nio: None
zarr: None
cftime: 1.5.1.1
nc_time_axis: None
PseudoNetCDF: None
rasterio: 1.2.10
cfgrib: None
iris: None
bottleneck: 1.3.4
dask: 2022.6.1
distributed: 2022.6.1
matplotlib: 3.5.1
cartopy: 0.20.2
seaborn: 0.11.2
numbagg: None
fsspec: 2022.3.0
cupy: None
pint: None
sparse: 0.13.0
flox: None
numpy_groupies: None
setuptools: 61.2.0
pip: 22.1.2
conda: 4.13.0
pytest: 7.1.2
IPython: 7.33.0
sphinx: 5.0.2
/home/fabian/.miniconda3/lib/python3.10/site-packages/_distutils_hack/init.py:30: UserWarning: Setuptools is replacing distutils.
warnings.warn("Setuptools is replacing distutils.")