TST: groupby apply with indexing and column aggregation returns the column #7002

pandas/tests/groupby/test_apply.py

@@ -155,6 +155,7 @@ def test_group_apply_once_per_group(df, group_names):
     # once per group
 
     names = []
+
     # cannot parameterize over the functions since they need external
     # `names` to detect side effects
 
@@ -683,7 +684,6 @@ def func_with_date(batch):
 
 
 def test_gb_apply_list_of_unequal_len_arrays():
-
     # GH1738
     df = DataFrame(
         {
@@ -961,3 +961,16 @@ def fn(x):
         name="col2",
     )
     tm.assert_series_equal(result, expected)
+
+
+def test_apply_function_with_indexing_return_column():
+    # GH: 7002
+    df = DataFrame(
+        {
+            "foo1": ["one", "two", "two", "three", "one", "two"],
+            "foo2": [1, 2, 4, 4, 5, 6],
+        }
+    )
+    result = df.groupby("foo1", as_index=False).apply(lambda x: x.mean())
+    expected = DataFrame({"foo1": ["one", "three", "two"], "foo2": [3.0, 4.0, 4.0]})
+    tm.assert_frame_equal(result, expected)