feat: implement anti-join, str.len_chars, and null_count for DuckDB (#…

…1777)


---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

narwhals/_arrow/dataframe.py

@@ -333,7 +333,7 @@ def join(
         self: Self,
         other: Self,
         *,
-        how: Literal["left", "inner", "outer", "cross", "anti", "semi"],
+        how: Literal["left", "inner", "cross", "anti", "semi"],
         left_on: str | list[str] | None,
         right_on: str | list[str] | None,
         suffix: str,

narwhals/_dask/dataframe.py

@@ -236,7 +236,7 @@ def join(
         self: Self,
         other: Self,
         *,
-        how: Literal["left", "inner", "outer", "cross", "anti", "semi"] = "inner",
+        how: Literal["left", "inner", "cross", "anti", "semi"] = "inner",
         left_on: str | list[str] | None,
         right_on: str | list[str] | None,
         suffix: str,

narwhals/_duckdb/dataframe.py

@@ -215,7 +215,7 @@ def join(
         self: Self,
         other: Self,
         *,
-        how: Literal["left", "inner", "outer", "cross", "anti", "semi"] = "inner",
+        how: Literal["left", "inner", "cross", "anti", "semi"] = "inner",
         left_on: str | list[str] | None,
         right_on: str | list[str] | None,
         suffix: str,
@@ -226,10 +226,6 @@ def join(
             right_on = [right_on]
         original_alias = self._native_frame.alias
 
-        if how not in ("inner", "left", "semi", "cross"):
-            msg = "Only inner and left join is implemented for DuckDB"
-            raise NotImplementedError(msg)
-
         if how == "cross":
             if self._backend_version < (1, 1, 4):
                 msg = f"DuckDB>=1.1.4 is required for cross-join, found version: {self._backend_version}"

narwhals/_duckdb/expr.py

@@ -1,6 +1,5 @@
 from __future__ import annotations
 
-import functools
 from typing import TYPE_CHECKING
 from typing import Any
 from typing import Callable
@@ -488,6 +487,15 @@ def min(self) -> Self:
             lambda _input: FunctionExpression("min", _input), "min", returns_scalar=True
         )
 
+    def null_count(self) -> Self:
+        from duckdb import FunctionExpression
+
+        return self._from_call(
+            lambda _input: FunctionExpression("sum", _input.isnull().cast("int")),
+            "null_count",
+            returns_scalar=True,
+        )
+
     def is_null(self) -> Self:
         return self._from_call(
             lambda _input: _input.isnull(), "is_null", returns_scalar=self._returns_scalar
@@ -497,11 +505,7 @@ def is_in(self, other: Sequence[Any]) -> Self:
         from duckdb import ConstantExpression
 
         return self._from_call(
-            lambda _input: functools.reduce(
-                lambda x, y: x | _input.isin(ConstantExpression(y)),
-                other[1:],
-                _input.isin(ConstantExpression(other[0])),
-            ),
+            lambda _input: _input.isin(*[ConstantExpression(x) for x in other]),
             "is_in",
             returns_scalar=self._returns_scalar,
         )
@@ -619,6 +623,15 @@ def func(_input: duckdb.Expression) -> duckdb.Expression:
             func, "slice", returns_scalar=self._compliant_expr._returns_scalar
         )
 
+    def len_chars(self) -> DuckDBExpr:
+        from duckdb import FunctionExpression
+
+        return self._compliant_expr._from_call(
+            lambda _input: FunctionExpression("length", _input),
+            "len_chars",
+            returns_scalar=self._compliant_expr._returns_scalar,
+        )
+
     def to_lowercase(self) -> DuckDBExpr:
         from duckdb import FunctionExpression
 

narwhals/_pandas_like/dataframe.py

@@ -512,7 +512,7 @@ def join(
         self,
         other: Self,
         *,
-        how: Literal["left", "inner", "outer", "cross", "anti", "semi"] = "inner",
+        how: Literal["left", "inner", "cross", "anti", "semi"] = "inner",
         left_on: str | list[str] | None,
         right_on: str | list[str] | None,
         suffix: str,

tests/expr_and_series/null_count_test.py

@@ -1,7 +1,5 @@
 from __future__ import annotations
 
-import pytest
-
 import narwhals.stable.v1 as nw
 from tests.utils import Constructor
 from tests.utils import ConstructorEager
@@ -13,11 +11,7 @@
 }
 
 
-def test_null_count_expr(
-    constructor: Constructor, request: pytest.FixtureRequest
-) -> None:
-    if "duckdb" in str(constructor):
-        request.applymarker(pytest.mark.xfail)
+def test_null_count_expr(constructor: Constructor) -> None:
     df = nw.from_native(constructor(data))
     result = df.select(nw.col("a", "b").null_count())
     expected = {

tests/expr_and_series/str/len_chars_test.py

@@ -1,7 +1,5 @@
 from __future__ import annotations
 
-import pytest
-
 import narwhals.stable.v1 as nw
 from tests.utils import Constructor
 from tests.utils import ConstructorEager
@@ -10,9 +8,7 @@
 data = {"a": ["foo", "foobar", "Café", "345", "東京"]}
 
 
-def test_str_len_chars(constructor: Constructor, request: pytest.FixtureRequest) -> None:
-    if "duckdb" in str(constructor):
-        request.applymarker(pytest.mark.xfail)
+def test_str_len_chars(constructor: Constructor) -> None:
     df = nw.from_native(constructor(data))
     result = df.select(nw.col("a").str.len_chars())
     expected = {

tests/frame/join_test.py

@@ -166,10 +166,7 @@ def test_anti_join(
     join_key: list[str],
     filter_expr: nw.Expr,
     expected: dict[str, list[Any]],
-    request: pytest.FixtureRequest,
 ) -> None:
-    if "duckdb" in str(constructor):
-        request.applymarker(pytest.mark.xfail)
     data = {"antananarivo": [1, 3, 2], "bob": [4, 4, 6], "zor ro": [7.0, 8, 9]}
     df = nw.from_native(constructor(data))
     other = df.filter(filter_expr)