refactor: Implement CompliantDataFrame.aggregate

#2223 (comment)

Author: dangotbanned

narwhals/_arrow/dataframe.py

@@ -358,9 +358,6 @@ def simple_select(self, *column_names: str) -> Self:
             self._native_frame.select(list(column_names)), validate_column_names=False
         )
 
-    def aggregate(self: ArrowDataFrame, *exprs: ArrowExpr) -> ArrowDataFrame:
-        return self.select(*exprs)
-
     def select(self: ArrowDataFrame, *exprs: ArrowExpr) -> ArrowDataFrame:
         new_series = self._evaluate_into_exprs(*exprs)
         if not new_series:

narwhals/_compliant/dataframe.py

@@ -46,14 +46,12 @@ def simple_select(self, *column_names: str) -> Self:
         """`select` where all args are column names."""
         ...
 
-    # NOTE: Can we remove this now?
-    # `DaskLazyFrame` is the only one not the same as `select`
     def aggregate(self, *exprs: Any) -> Self:  # pragma: no cover
         """`select` where all args are aggregations or literals.
 
         (so, no broadcasting is necessary).
         """
-        ...
+        return self.select(*exprs)
 
     @property
     def columns(self) -> Sequence[str]: ...

narwhals/_pandas_like/dataframe.py

@@ -396,11 +396,6 @@ def simple_select(self: Self, *column_names: str) -> Self:
             validate_column_names=False,
         )
 
-    def aggregate(
-        self: PandasLikeDataFrame, *exprs: PandasLikeExpr
-    ) -> PandasLikeDataFrame:
-        return self.select(*exprs)
-
     def select(self: PandasLikeDataFrame, *exprs: PandasLikeExpr) -> PandasLikeDataFrame:
         new_series = self._evaluate_into_exprs(*exprs)
         if not new_series: