issues

What happened?

Got a TypeError when resampling a dataset along a dimension, mapping a function to each group. The function returns a DataArray.

Failed with : TypeError: _overwrite_indexes() got an unexpected keyword argument 'variables'

What did you expect to happen?

This worked before the merging of #5692. A DataArray was returned as expected.

Minimal Complete Verifiable Example

```Python import xarray as xr

ds = xr.tutorial.open_dataset("air_temperature")

ds.resample(time="YS").map(lambda grp: grp.air.mean("time")) ```

Relevant log output

```Python

TypeError Traceback (most recent call last) Input In [37], in <module> ----> 1 ds.resample(time="YS").map(lambda grp: grp.air.mean("time"))

File /opt/miniconda3/envs/xclim-pip/lib/python3.9/site-packages/xarray/core/resample.py:300, in DatasetResample.map(self, func, args, shortcut, kwargs) 298 # ignore shortcut if set (for now) 299 applied = (func(ds, *args, kwargs) for ds in self._iter_grouped()) --> 300 combined = self._combine(applied) 302 return combined.rename({self._resample_dim: self._dim})

File /opt/miniconda3/envs/xclim-pip/lib/python3.9/site-packages/xarray/core/groupby.py:999, in DatasetGroupByBase._combine(self, applied) 997 index, index_vars = create_default_index_implicit(coord) 998 indexes = {k: index for k in index_vars} --> 999 combined = combined._overwrite_indexes(indexes, variables=index_vars) 1000 combined = self._maybe_restore_empty_groups(combined) 1001 combined = self._maybe_unstack(combined)

TypeError: _overwrite_indexes() got an unexpected keyword argument 'variables' ```

Anything else we need to know?

In the docstring of DatasetGroupBy.map it is not made clear that the passed function should return a dataset, but the opposite is also not said. This worked before and I think the issues comes from #5692, which introduced different signatures for DataArray._overwrite_indexes (which is called in my case) and Dataset._overwrite_indexes (which is expected by the new _combine).

If the function passed to Dataset.resample(...).map should only return Datasets then I believe a more explicit error is needed, as well as some notice in the docs and a breaking change entry in the changelog. If DataArrays should be accepted, then we have a regression here.

I may have time to help on this.

Environment

What happened?

When concatenating two objects with xr.concat along a new dimension given through a DataArray, the attributes of this given coordinate are lost in the concatenation.

What did you expect to happen?

I expected the concatenation coordinate to be identical to the 1D DataArray I gave to concat.

Minimal Complete Verifiable Example

```Python import xarray as xr

ds = xr.tutorial.open_dataset("air_temperature")

concat_dim = xr.DataArray([1, 2], dims=("condim",), attrs={"an_attr": "yep"}, name="condim")

out = xr.concat([ds, ds], concat_dim) out.condim.attrs ```

Before #5692, I get: {'an_attr': 'yep'} with the current master, I get: {}

Anything else we need to know?

I'm not 100% sure, but I think the change is due to xr.core.concat._calc_concat_dim_coord being replaced by xr.core.concat.__calc_concat_dim_index. The former didn't touch the concatenation coordinate, while the latter casts it as an index, thus dropping the attributes in the process.

If the solution is to add a check in xr.concat, I may have time to implement something simple.

Environment