Polyfit with weights doesn't work with one-dimensional array

[mgunyho]

What happened?

I'm trying to use DataArray.polyfit with a set of weights, but if the data is one-dimensional, I get the following error:

Traceback (most recent call last):
  File ".../xarray/.scratch/polyfit-1d-weights.py", line 3, in <module>
    xr.DataArray([1, 2, 4], coords=[("x", [1, 2, 3])]).polyfit("x", deg=2, w=[0.1, 0.2, 0.3])
  File ".../xarray/xarray/core/dataarray.py", line 5729, in polyfit
    return self._to_temp_dataset().polyfit(
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".../xarray/xarray/core/dataset.py", line 9223, in polyfit
    rhs = rhs * w[:, np.newaxis]
          ~~~~^~~~~~~~~~~~~~~~~~
  File ".../xarray/xarray/core/_typed_ops.py", line 934, in __mul__
    return self._binary_op(other, operator.mul)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".../xarray/xarray/core/variable.py", line 2393, in _binary_op
    result = Variable(dims, new_data, attrs=attrs)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".../xarray/xarray/core/variable.py", line 424, in __init__
    super().__init__(
  File ".../xarray/xarray/namedarray/core.py", line 264, in __init__
    self._dims = self._parse_dimensions(dims)
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".../xarray/xarray/namedarray/core.py", line 508, in _parse_dimensions
    raise ValueError(
ValueError: dimensions ('x',) must have the same length as the number of data dimensions, ndim=2

What did you expect to happen?

Polyfit should work normally when both the input data and weights are one-dimensional

Minimal Complete Verifiable Example

import xarray as xr

xr.DataArray([1, 2, 4], coords=[("x", [1, 2, 3])]).polyfit("x", deg=2, w=[0.1, 0.2, 0.3])

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.
• Recent environment — the issue occurs with the latest version of xarray and its dependencies.

Relevant log output

No response

Anything else we need to know?

If I artificially add an extra dimension to the data, there is no error. For example, the following works:

(
     xr.DataArray([1, 2, 4], coords=[("x", [1, 2, 3])])
     .expand_dims(foo=1)
     .polyfit("x", deg=2, w=[0.1, 0.2, 0.3])
 )

Environment

INSTALLED VERSIONS

commit: None
python: 3.12.7 (main, Oct 1 2024, 00:00:00) [GCC 14.2.1 20240912 (Red Hat 14.2.1-3)]
python-bits: 64
OS: Linux
OS-release: 6.11.5-200.fc40.x86_64
machine: x86_64
processor:
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8
LOCALE: ('en_US', 'UTF-8')
libhdf5: None
libnetcdf: None

xarray: 2024.9.1.dev73+g8f6e45ba
pandas: 2.2.3
numpy: 2.1.2
scipy: None
netCDF4: None
pydap: None
h5netcdf: None
h5py: None
zarr: None
cftime: None
nc_time_axis: None
iris: None
bottleneck: None
dask: None
distributed: None
matplotlib: None
cartopy: None
seaborn: None
numbagg: None
fsspec: None
cupy: None
pint: None
sparse: None
flox: None
numpy_groupies: None
setuptools: None
pip: 23.3.2
conda: None
pytest: None
mypy: None
IPython: None
sphinx: None