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Fix writing/reading for subsecond outputdt #2806

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Fix writing/reading for subsecond outputdt #2806

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98ce13d
Adding unit test for writing/reading subsecond outputdt
erikvansebille Aug 6, 2026
f835780
Adding unit test
erikvansebille Aug 6, 2026
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2 changes: 1 addition & 1 deletion src/parcels/_core/particlefile.py
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Original file line number Diff line number Diff line change
Expand Up @@ -275,7 +275,7 @@ def read_particlefile(path: PathLike, decode_times: bool = True) -> pd.DataFrame

values = table.column("t").to_numpy()
var = xr.Variable(("t",), values, attrs)
values = xr.coders.CFDatetimeCoder(time_unit="s").decode(var).values
values = xr.coders.CFDatetimeCoder(time_unit="ns").decode(var).values
if "since" in attrs["units"]:
values = values.astype("datetime64[ns]")
df = df.with_columns(pl.Series("t", values, dtype=pl.Datetime("ns")))
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18 changes: 18 additions & 0 deletions tests/test_particlefile.py
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Expand Up @@ -344,6 +344,24 @@ def Update_lon(particles, fieldset): # pragma: no cover
assert np.allclose(pset.x, 0.6)


@pytest.mark.parametrize("dt", [100, 200])
def test_subsecond_outputdt(fieldset, dt, tmp_parquet):
"""Test that outputdt can be subsecond and that the output times are correct."""

def Update_lon(particles, fieldset): # pragma: no cover
particles.dx += dt / 1000.0 # Move at a rate of 1 unit per second

pset = ParticleSet(fieldset, x=[0], y=[0])
ofile = ParticleFile(tmp_parquet, outputdt=np.timedelta64(dt, "ms"))
pset.execute(Update_lon, runtime=np.timedelta64(1, "s"), dt=np.timedelta64(dt, "ms"), output_file=ofile)

df = parcels.read_particlefile(tmp_parquet)
np.testing.assert_allclose(df["x"], np.arange(0, 1 + 1e-6, dt / 1000.0), atol=1e-6)
expected_t = np.arange(0, 1001, dt).astype("timedelta64[ms]")
elapsed_t = (df["t"] - df["t"].min()).to_numpy().astype("timedelta64[ms]")
np.testing.assert_allclose(elapsed_t, expected_t, atol=1)


def test_correct_misaligned_outputdt_dt(fieldset, tmp_parquet):
"""Testing that outputdt does not need to be a multiple of dt."""

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