feat: add duckdb dataframe drop_nulls (#1811)

* feat: add duckdb dataframe drop_nulls

* rollback

* test columns with spaces

* single double quote

* push list conversion to narwhals BaseFrame level

narwhals/_arrow/dataframe.py

@@ -395,10 +395,9 @@ def drop(self: Self, columns: list[str], strict: bool) -> Self:  # noqa: FBT001
         )
         return self._from_native_frame(self._native_frame.drop(to_drop))
 
-    def drop_nulls(self: Self, subset: str | list[str] | None) -> Self:
+    def drop_nulls(self: Self, subset: list[str] | None) -> Self:
         if subset is None:
             return self._from_native_frame(self._native_frame.drop_null())
-        subset = [subset] if isinstance(subset, str) else subset
         plx = self.__narwhals_namespace__()
         return self.filter(~plx.any_horizontal(plx.col(*subset).is_null()))
 

narwhals/_dask/dataframe.py

@@ -149,10 +149,9 @@ def select(
         )
         return self._from_native_frame(df)
 
-    def drop_nulls(self: Self, subset: str | list[str] | None) -> Self:
+    def drop_nulls(self: Self, subset: list[str] | None) -> Self:
         if subset is None:
             return self._from_native_frame(self._native_frame.dropna())
-        subset = [subset] if isinstance(subset, str) else subset
         plx = self.__narwhals_namespace__()
         return self.filter(~plx.any_horizontal(plx.col(*subset).is_null()))
 

narwhals/_duckdb/dataframe.py

@@ -321,3 +321,12 @@ def sort(
             )
         )
         return self._from_native_frame(result)
+
+    def drop_nulls(self: Self, subset: list[str] | None) -> Self:
+        import duckdb
+
+        rel = self._native_frame
+        subset_ = subset if subset is not None else rel.columns
+        keep_condition = " and ".join(f'"{col}" is not null' for col in subset_)
+        query = f"select * from rel where {keep_condition}"  # noqa: S608
+        return self._from_native_frame(duckdb.sql(query))

narwhals/_pandas_like/dataframe.py

@@ -371,10 +371,9 @@ def select(
         )
         return self._from_native_frame(df)
 
-    def drop_nulls(self, subset: str | list[str] | None) -> Self:
+    def drop_nulls(self, subset: list[str] | None) -> Self:
         if subset is None:
             return self._from_native_frame(self._native_frame.dropna(axis=0))
-        subset = [subset] if isinstance(subset, str) else subset
         plx = self.__narwhals_namespace__()
         return self.filter(~plx.any_horizontal(plx.col(*subset).is_null()))
 

narwhals/_spark_like/dataframe.py

@@ -183,7 +183,7 @@ def sort(
         sort_cols = [sort_f(col) for col, sort_f in zip(flat_by, sort_funcs)]
         return self._from_native_frame(self._native_frame.sort(*sort_cols))
 
-    def drop_nulls(self: Self, subset: str | list[str] | None) -> Self:
+    def drop_nulls(self: Self, subset: list[str] | None) -> Self:
         return self._from_native_frame(self._native_frame.dropna(subset=subset))
 
     def rename(self: Self, mapping: dict[str, str]) -> Self:

narwhals/dataframe.py

@@ -107,7 +107,8 @@ def with_row_index(self, name: str = "index") -> Self:
             self._compliant_frame.with_row_index(name),
         )
 
-    def drop_nulls(self: Self, subset: str | list[str] | None = None) -> Self:
+    def drop_nulls(self: Self, subset: str | list[str] | None) -> Self:
+        subset = [subset] if isinstance(subset, str) else subset
         return self._from_compliant_dataframe(
             self._compliant_frame.drop_nulls(subset=subset),
         )

tests/frame/drop_nulls_test.py

@@ -7,37 +7,32 @@
 from tests.utils import assert_equal_data
 
 data = {
-    "a": [1.0, 2.0, None, 4.0],
-    "b": [None, 3.0, None, 5.0],
+    "alpha": [1.0, 2.0, None, 4.0],
+    "beta gamma": [None, 3.0, None, 5.0],
 }
 
 
-def test_drop_nulls(constructor: Constructor, request: pytest.FixtureRequest) -> None:
-    if "duckdb" in str(constructor):
-        request.applymarker(pytest.mark.xfail)
+def test_drop_nulls(constructor: Constructor) -> None:
     result = nw.from_native(constructor(data)).drop_nulls()
     expected = {
-        "a": [2.0, 4.0],
-        "b": [3.0, 5.0],
+        "alpha": [2.0, 4.0],
+        "beta gamma": [3.0, 5.0],
     }
     assert_equal_data(result, expected)
 
 
 @pytest.mark.parametrize(
     ("subset", "expected"),
     [
-        ("a", {"a": [1, 2.0, 4.0], "b": [None, 3.0, 5.0]}),
-        (["a"], {"a": [1, 2.0, 4.0], "b": [None, 3.0, 5.0]}),
-        (["a", "b"], {"a": [2.0, 4.0], "b": [3.0, 5.0]}),
+        ("alpha", {"alpha": [1, 2.0, 4.0], "beta gamma": [None, 3.0, 5.0]}),
+        (["alpha"], {"alpha": [1, 2.0, 4.0], "beta gamma": [None, 3.0, 5.0]}),
+        (["alpha", "beta gamma"], {"alpha": [2.0, 4.0], "beta gamma": [3.0, 5.0]}),
     ],
 )
 def test_drop_nulls_subset(
     constructor: Constructor,
     subset: str | list[str],
     expected: dict[str, float],
-    request: pytest.FixtureRequest,
 ) -> None:
-    if "duckdb" in str(constructor):
-        request.applymarker(pytest.mark.xfail)
     result = nw.from_native(constructor(data)).drop_nulls(subset=subset)
     assert_equal_data(result, expected)