BUG: DataFrame.aggregate returns Series for empty DataFrame with single function

Author: RI-Jeyaprathap

pandas/core/frame.py

@@ -10501,14 +10501,24 @@ def _gotitem(
     )
     def aggregate(self, func=None, axis: Axis = 0, *args, **kwargs):
         from pandas.core.apply import frame_apply
-
+        from pandas import Series
         axis = self._get_axis_number(axis)
-
+        # Special case: empty DataFrame + single function
+        if self.empty and callable(func):
+            if axis == 1:  # row-wise
+                return Series([], index=self.index, dtype=object)
+            else:  # column-wise
+                # Column-wise on empty DataFrame -> empty Series
+                return Series([], dtype=object)
+
+        # Normal behavior
         op = frame_apply(self, func=func, axis=axis, args=args, kwargs=kwargs)
         result = op.agg()
         result = reconstruct_and_relabel_result(result, func, **kwargs)
         return result
 
+
+
     agg = aggregate
 
     @doc(

pandas/tests/frame/methods/test_aggregate.py

@@ -0,0 +1,11 @@
+def test_aggregate_empty_dataframe_returns_series():
+    import pandas as pd
+    df = pd.DataFrame({"A": [], "B": []})
+    # Row-wise aggregation (axis=1)
+    result_row = df.aggregate(".".join, axis="columns")
+    expected_row = pd.Series([], index=df.index, dtype=object)
+    pd.testing.assert_series_equal(result_row, expected_row)
+    # Column-wise aggregation (axis=0)
+    result_col = df.aggregate(".".join, axis="index")
+    expected_col = pd.Series([], dtype=object)
+    pd.testing.assert_series_equal(result_col, expected_col)