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Warn when grouping by dask array. #6788

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Warn when grouping by dask array. #6788

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Warn when grouping by dask array.
dcherian Jul 15, 2022
d752672
FIx mypy?
dcherian Jul 15, 2022
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12 changes: 11 additions & 1 deletion xarray/core/groupby.py
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Original file line number Diff line number Diff line change
Expand Up @@ -29,7 +29,7 @@
from .indexes import create_default_index_implicit, filter_indexes_from_coords
from .npcompat import QUANTILE_METHODS, ArrayLike
from .options import _get_keep_attrs
from .pycompat import integer_types
from .pycompat import integer_types, is_duck_dask_array
from .types import T_Xarray
from .utils import (
either_dict_or_kwargs,
Expand Down Expand Up @@ -377,6 +377,16 @@ def __init__(
self._unstacked_group = group
self._bins = bins

if not isinstance(group, _DummyGroup) and is_duck_dask_array(group.data):
warnings.warn(
"Grouping by a dask array computes that array. "
"This will raise an error in the future. "
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My naive dream would have been that it successfully grouped the dask array lazily in the future. But that's maybe for the even further future if even possible?

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@dcherian dcherian Jul 15, 2022 •
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🤦 I don't know what I was thinking...

Yes we can now do that with flox...

"Use `.groupby(group.compute())` to avoid an error in the future.",
UserWarning,
stacklevel=3,
)
group = group.compute()

group, obj, stacked_dim, inserted_dims = _ensure_1d(group, obj)
(group_dim,) = group.dims

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7 changes: 7 additions & 0 deletions xarray/tests/test_groupby.py
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Original file line number Diff line number Diff line change
Expand Up @@ -504,6 +504,13 @@ def test_groupby_repr_datetime(obj) -> None:
assert actual == expected


@requires_dask
def test_groupby_dask_array_raises_warning():
ds = Dataset({"foo": ("x", np.arange(10)), "baz": ("x", np.arange(10))}).chunk()
with pytest.warns(UserWarning):
ds.groupby("baz")


def test_groupby_drops_nans() -> None:
# GH2383
# nan in 2D data variable (requires stacking)
Expand Down