done

lib/python3.11/site-packages/narwhals/_duckdb/group_by.py

@@ -0,0 +1,33 @@
+from __future__ import annotations
+
+from itertools import chain
+from typing import TYPE_CHECKING
+
+from narwhals._sql.group_by import SQLGroupBy
+
+if TYPE_CHECKING:
+    from collections.abc import Sequence
+
+    from duckdb import Expression  # noqa: F401
+
+    from narwhals._duckdb.dataframe import DuckDBLazyFrame
+    from narwhals._duckdb.expr import DuckDBExpr
+
+
+class DuckDBGroupBy(SQLGroupBy["DuckDBLazyFrame", "DuckDBExpr", "Expression"]):
+    def __init__(
+        self,
+        df: DuckDBLazyFrame,
+        keys: Sequence[DuckDBExpr] | Sequence[str],
+        /,
+        *,
+        drop_null_keys: bool,
+    ) -> None:
+        frame, self._keys, self._output_key_names = self._parse_keys(df, keys=keys)
+        self._compliant_frame = frame.drop_nulls(self._keys) if drop_null_keys else frame
+
+    def agg(self, *exprs: DuckDBExpr) -> DuckDBLazyFrame:
+        agg_columns = list(chain(self._keys, self._evaluate_exprs(exprs)))
+        return self.compliant._with_native(
+            self.compliant.native.aggregate(agg_columns)  # type: ignore[arg-type]
+        ).rename(dict(zip(self._keys, self._output_key_names)))