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

Author: RI-Jeyaprathap

.gitignore

@@ -141,4 +141,4 @@ doc/source/savefig/
 # Pyodide/WASM related files #
 ##############################
 /.pyodide-xbuildenv-*
-venv/ 
+venv/

pandas/core/frame.py

@@ -10503,6 +10503,13 @@ def aggregate(self, func=None, axis: Axis = 0, *args, **kwargs):
         from pandas.core.apply import frame_apply
 
         axis = self._get_axis_number(axis)
+        if self.empty and callable(func):
+            if axis == 1:
+                return Series([None] * len(self.index), index=self.index, dtype=object)
+            else:
+                return Series(
+                    [None] * len(self.columns), index=self.columns, dtype=object
+                )
 
         op = frame_apply(self, func=func, axis=axis, args=args, kwargs=kwargs)
         result = op.agg()

pandas/tests/frame/methods/test_aggregate.py

@@ -0,0 +1,12 @@
+import pandas as pd
+import pandas._testing as tm
+
+
+def test_aggregate_empty_dataframe_returns_series():
+    df = pd.DataFrame({"A": [], "B": []})
+    result_row = df.aggregate(".".join, axis="columns")
+    expected_row = pd.Series([None] * len(df.index), index=df.index, dtype=object)
+    tm.assert_series_equal(result_row, expected_row)
+    result_col = df.aggregate(".".join, axis="index")
+    expected_col = pd.Series([None] * len(df.columns), index=df.columns, dtype=object)
+    tm.assert_series_equal(result_col, expected_col)