Fix crosstab(aggfunc='skew') bug

Fix `IndexError` in `crosstab` with `aggfunc=‘skew’`.

* Check if table is empty before accessing last row in `_normalize` function in `pandas/core/reshape/pivot.py`.
* Skip normalization and return empty table if it is.
* Add test case in `pandas/tests/reshape/test_crosstab.py` for `aggfunc=‘skew’`.
* Ensure test case doesn’t raise `IndexError`.

Author: Vishnu-sai-teja

pandas/core/reshape/pivot.py

@@ -1144,6 +1144,10 @@ def _normalize(
         # keep index and column of pivoted table
         table_index = table.index
         table_columns = table.columns
+
+        if table.empty:
+            return table
+
         last_ind_or_col = table.iloc[-1, :].name
 
         # check if margin name is not in (for MI cases) and not equal to last

pandas/tests/reshape/test_crosstab.py

@@ -877,3 +877,17 @@ def test_categoricals(a_dtype, b_dtype):
         expected = expected.loc[[0, 2, "All"]]
         expected["All"] = expected["All"].astype("int64")
     tm.assert_frame_equal(result, expected)
+
+def test_crosstab_aggfunc_skew():
+    # Test case for crosstab with aggfunc='skew'
+    result = crosstab(
+        index=["index1", "index2"],
+        columns=["one", "one"],
+        values=[12, 10],
+        normalize=1,
+        margins=True,
+        dropna=True,
+        aggfunc='skew'
+    )
+    assert isinstance(result, DataFrame)
+    assert not result.empty