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Merged
dcherian merged 2 commits into from
Mar 27, 2026
Merged

Avoid overlapping bounds and/or gaps when points are irregularly spaced #622

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5969389
Avoid overlapping bounds when points are irregularly spaced
bouweandela Mar 24, 2026
a9e143a
Merge branch 'main' into avoid-overlapping-bounds
dcherian Mar 27, 2026
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17 changes: 9 additions & 8 deletions cf_xarray/helpers.py
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Original file line number Diff line number Diff line change
Expand Up @@ -23,15 +23,16 @@ def _guess_bounds_1d(da, dim):
da = da.assign_coords({dim: da[dim]})
ADDED_INDEX = True

diff = da.diff(dim)
lower = da - diff / 2
upper = da + diff / 2
bounds = xr.concat([lower, upper], dim="bounds")
bound_position = 0.5
diff = da.diff(dim).pad({dim: (1, 1)}, mode="edge").reset_index(dim)
lower = (
da.reset_index(dim) - bound_position * diff.isel({dim: slice(0, -1)})
).assign_coords({dim: da[dim]})
upper = (
da.reset_index(dim) + bound_position * diff.isel({dim: slice(1, None)})
).assign_coords({dim: da[dim]})
Comment on lines +28 to +33
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@dcherian dcherian Mar 27, 2026

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oops, merged too early.

we could optimize here by calling reset_index once and assigning coords to result directly

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@bouweandela bouweandela Mar 30, 2026

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No worries, I'm happy to continue working on this. I'm still pretty new to xarray, but I think I found a better way to do this and opened a pull request in #627.

result = xr.concat([lower, upper], dim="bounds").transpose(..., "bounds")

first = (bounds.isel({dim: 0}) - diff.isel({dim: 0})).assign_coords(
{dim: da[dim][0]}
)
result = xr.concat([first, bounds], dim=dim).transpose(..., "bounds")
if ADDED_INDEX:
result = result.drop_vars(dim)
return result.drop_attrs(deep=False)
Expand Down
34 changes: 32 additions & 2 deletions cf_xarray/tests/test_accessor.py
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Original file line number Diff line number Diff line change
Expand Up @@ -839,6 +839,36 @@ def test_add_bounds(dims):
_check_unchanged(original, ds)


def test_add_irregularly_spaced_bounds_do_not_overlap() -> None:
# Test that added bounds with irregular spacing do not overlap.
ds = airds
original = ds.copy(deep=True)
ds["time"] = ds["time"].copy(data=pd.date_range("2013-01", "2013-04", freq="MS"))
expected = xr.DataArray(
data=[
pd.to_datetime(t)
for t in [
["2012-12-16T12", "2013-01-16T12"],
["2013-01-16T12", "2013-02-15T00"],
["2013-02-15T00", "2013-03-16T12"],
["2013-03-16T12", "2013-04-16T12"],
]
],
dims=["time", "bounds"],
name="time_bounds",
coords={"time": ds.time.data},
)
added = ds.copy(deep=False)
added = added.cf.add_bounds("time")

name = "time_bounds"
assert name in added.coords
assert added["time"].attrs["bounds"] == name
assert_allclose(added[name].reset_coords(drop=True), expected)

_check_unchanged(original, ds)


def test_add_bounds_multiple() -> None:
# Test multiple dimensions
assert not {"x1_bounds", "x2_bounds"} <= set(multiple.variables)
Expand Down Expand Up @@ -882,11 +912,11 @@ def test_add_bounds_nd_variable() -> None:
expected = (
xr.concat([ds.z - 1.5, ds.z + 1.5], dim="bounds")
.rename("z_bounds")
.transpose("bounds", "y", "x")
.transpose(..., "bounds")
)

actual = ds.cf.add_bounds("z", dim="x").z_bounds.reset_coords(drop=True)
xr.testing.assert_identical(expected.transpose(..., "bounds"), actual)
xr.testing.assert_identical(expected, actual)

# Requesting bounds on a non-variable dimension
with pytest.raises(ValueError, match="are dimensions with no index."):
Expand Down