weighted polyfit with NaNs appears broken

[bbuzz31]

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What happened?

polyfit can't seem to handle weights still (despite https://github.com/pydata/xarray/pull/5933). nans are involved.

What did you expect to happen?

No response

Minimal Complete Verifiable Example

np.random.seed(10)
y = np.random.rand(10)
x = np.arange(len(y))
y[3] = np.nan
y[5] = np.nan
w = y/10

msk = ~np.isnan(y)
x = x[msk]
y = y[msk]
w = w[msk]

da_test = xr.DataArray(y, dims='time', coords={'time': x})
da_test.polyfit('time', 1, w=w)

# np.polyfit(x, y, 1)#, w=w) # <-- should match this

MVCE confirmation

• [X] Minimal example — the example is as focused as reasonably possible to demonstrate the underlying issue in xarray.
• [X] 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?

not inserting the nans and/or converting the weights to a data array didn't matter

Environment

INSTALLED VERSIONS

commit: None python: 3.12.3 | packaged by conda-forge | (main, Apr 15 2024, 18:38:13) [GCC 12.3.0] python-bits: 64 OS: Linux OS-release: 5.14.0-284.30.1.el9_2.x86_64 machine: x86_64 processor: x86_64 byteorder: little LC_ALL: None LANG: en_US.UTF-8 LOCALE: ('en_US', 'UTF-8') libhdf5: 1.14.3 libnetcdf: 4.9.2

xarray: 2024.3.0 pandas: 2.2.2 numpy: 1.26.4 scipy: 1.13.0 netCDF4: 1.6.5 pydap: None h5netcdf: 1.3.0 h5py: 3.11.0 Nio: None zarr: None cftime: 1.6.3 nc_time_axis: None iris: None bottleneck: None dask: 2024.5.0 distributed: 2024.5.0 matplotlib: 3.8.4 cartopy: 0.23.0 seaborn: 0.13.2 numbagg: None fsspec: 2024.3.1 cupy: None pint: None sparse: None flox: None numpy_groupies: None setuptools: 69.5.1 pip: 24.0 conda: None pytest: None mypy: None IPython: 8.22.2 sphinx: None

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[gcaria]

This seems to be alright now

   ...: da_test.polyfit('time', 1, w=w)
Out[4]:
<xarray.Dataset> Size: 32B
Dimensions:               (degree: 2)
Coordinates:
  * degree                (degree) int64 16B 1 0
Data variables:
    polyfit_coefficients  (degree) float64 16B -0.009755 0.7121

In [5]: np.polyfit(x, y, 1, w=w)
Out[5]: array([-0.00975477,  0.71212604])