code sample for pandas-dev#45315

Author: simonjayhawkins

bisect/45315.py

@@ -0,0 +1,17 @@
+# Behavior change of 1.4.rc0 when group by apply returns a copy of the passed data frame #45315
+
+import pandas as pd
+
+print(pd.__version__)
+
+df = pd.DataFrame([[1, 2, 3, 4]], columns=["A", "B", "C", "D"])
+grouped = df.groupby(["A", "B"], as_index=True)[["C", "D"]]
+
+combined = grouped.apply(lambda x: x.copy())
+print(combined)
+
+result = combined.reset_index().columns
+print(result)
+
+expected = pd.Index(["A", "B", "level_2", "C", "D"], dtype="object")
+pd.testing.assert_index_equal(result, expected)