Reports

Grouping by multiple arrays is now natively supported since Xarray>=2024.09.0.

https://xarray.dev/blog/multiple-groupers#more-complex-time-grouping

import xarray as xr


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

ds.groupby(["time.year", "time.month"]).mean()

I think your real problem is solved by "resampling", for which we support complex season definitions now (Xarray >2025.04.0):

import xarray as xr
from xarray.groupers import SeasonResampler

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

ds.resample(time=SeasonResampler(["DJFM", "AMJ", "SON"])).mean()

https://docs.xarray.dev/en/latest/user-guide/time-series.html#handling-seasons

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