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feat(let): add strftime function #1373

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302b1b6
feat(let): add strftime function
mesejo Nov 5, 2025
abbcd48
chore: use dt.string
mesejo Nov 6, 2025
e5b5123
fix: cast to StringArray, so it is clear the type expected
mesejo Nov 6, 2025
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4 changes: 3 additions & 1 deletion python/xorq/backends/let/datafusion/compiler.py
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Original file line number Diff line number Diff line change
Expand Up @@ -93,7 +93,6 @@ class DataFusionCompiler(SQLGlotCompiler):
ops.CountDistinctStar,
ops.DateDelta,
ops.RowID,
ops.Strftime,
ops.TimeDelta,
ops.TimestampDelta,
)
Expand Down Expand Up @@ -664,5 +663,8 @@ def visit_ArrayAny(self, op, *, arg):
),
)

def visit_Strftime(self, op, *, arg, format_str):
return self.f.temporal_strftime(arg, format_str)


compiler = DataFusionCompiler()
12 changes: 12 additions & 0 deletions python/xorq/backends/let/datafusion/udfs.py
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Original file line number Diff line number Diff line change
@@ -1,6 +1,7 @@
from __future__ import annotations

import itertools
import typing
from urllib.parse import parse_qs, urlsplit

import pyarrow as pa
Expand Down Expand Up @@ -129,3 +130,14 @@ def regex_split(s: str, pattern: str) -> list[str]:
)
pattern = patterns[0].as_py()
return pc.split_pattern_regex(s, pattern)


def temporal_strftime(array: dt.Timestamp(scale=9), pattern: dt.string) -> dt.string:
pattern, *_rest = typing.cast(pa.StringArray, pattern).unique().to_pylist()

if len(_rest) > 0:
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@dlovell dlovell Nov 10, 2025

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let's use "truth value testing" here: if rest:
https://docs.python.org/3/library/stdtypes.html#truth-value-testing

raise com.XorqError(
"Only a single scalar pattern is supported for DataFusion strftime"
)

return pc.strftime(array, pattern)
18 changes: 18 additions & 0 deletions python/xorq/backends/let/tests/test_temporal.py
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Expand Up @@ -158,6 +158,24 @@ def test_timestamp_extract_week_of_year(alltypes, alltypes_df):
assert_series_equal(result, expected)


@pytest.mark.parametrize(
("expr_fn", "pandas_pattern"),
[
param(
lambda t: t.timestamp_col.strftime("%Y%m%d").name("formatted"),
"%Y%m%d",
id="literal_format_str",
),
],
)
def test_strftime(alltypes, alltypes_df, expr_fn, pandas_pattern):
expr = expr_fn(alltypes)
expected = alltypes_df.timestamp_col.dt.strftime(pandas_pattern).rename("formatted")

result = expr.execute()
assert_series_equal(result, expected)


PANDAS_UNITS = {
"m": "Min",
"ms": "L",
Expand Down