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/6597#issuecomment-1124868221,https://api.github.com/repos/pydata/xarray/issues/6597,1124868221,IC_kwDOAMm_X85DDCB9,43316012,2022-05-12T11:18:14Z,2022-05-12T11:18:14Z,COLLABORATOR,"Ok, the first idea does not work since values is a numpy array.

The second idea should work, so this is a bug.
It seems that polyval does not work with timedeltas, I will look into that.","{""total_count"": 2, ""+1"": 2, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,1233717699
https://github.com/pydata/xarray/issues/6597#issuecomment-1124863541,https://api.github.com/repos/pydata/xarray/issues/6597,1124863541,IC_kwDOAMm_X85DDA41,22245117,2022-05-12T11:12:39Z,2022-05-12T11:12:39Z,CONTRIBUTOR,"Thanks - I think I might be misunderstanding how the new implementation works.
I tried the following changes, but both of them return an error:
```python
xr.polyval(values - values[0], polyfit_coefficients)
```
```
Traceback (most recent call last):
  File ""/Users/mattia/MyGit/test.py"", line 31, in <module>
    xr.polyval(values - values[0], polyfit_coefficients)
  File ""/Users/mattia/MyGit/xarray/xarray/core/computation.py"", line 1908, in polyval
    coord = _ensure_numeric(coord)  # type: ignore # https://github.com/python/mypy/issues/1533 ?
  File ""/Users/mattia/MyGit/xarray/xarray/core/computation.py"", line 1949, in _ensure_numeric
    return to_floatable(data)
  File ""/Users/mattia/MyGit/xarray/xarray/core/computation.py"", line 1939, in to_floatable
    x.data,
ValueError: cannot include dtype 'm' in a buffer
```

```python
xr.polyval(azimuth_time.coords[""azimuth_time""], polyfit_coefficients)
```
```
Traceback (most recent call last):
  File ""/Users/mattia/MyGit/test.py"", line 31, in <module>
    xr.polyval(azimuth_time.coords[""azimuth_time""], polyfit_coefficients)
  File ""/Users/mattia/MyGit/xarray/xarray/core/computation.py"", line 1908, in polyval
    coord = _ensure_numeric(coord)  # type: ignore # https://github.com/python/mypy/issues/1533 ?
  File ""/Users/mattia/MyGit/xarray/xarray/core/computation.py"", line 1949, in _ensure_numeric
    return to_floatable(data)
  File ""/Users/mattia/MyGit/xarray/xarray/core/computation.py"", line 1938, in to_floatable
    data=datetime_to_numeric(
  File ""/Users/mattia/MyGit/xarray/xarray/core/duck_array_ops.py"", line 434, in datetime_to_numeric
    array = array - offset
numpy.core._exceptions._UFuncBinaryResolutionError: ufunc 'subtract' cannot use operands with types dtype('<m8[ns]') and dtype('<M8[D]')
```","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,1233717699
https://github.com/pydata/xarray/issues/6597#issuecomment-1124854798,https://api.github.com/repos/pydata/xarray/issues/6597,1124854798,IC_kwDOAMm_X85DC-wO,43316012,2022-05-12T11:02:55Z,2022-05-12T11:04:28Z,COLLABORATOR,"As listed in breaking changes, the new polyval algorithm uses the values of the `coord` argument and not the index coordinate.

Your coordinate is a Timedelta `values -values[0]`, try using that directly or `azimuth_time.coords[""azimuth_time""]`.","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,1233717699