TST: ensure groupby get by index pandas-dev#33439

Author: sam-cohan

pandas/tests/groupby/test_groupby.py

@@ -2012,3 +2012,15 @@ def test_groups_repr_truncates(max_seq_items, expected):
 
         result = df.groupby(np.array(df.a)).groups.__repr__()
         assert result == expected
+
+def test_groupby_get_by_index():
+    # GH 33439
+    df = pd.DataFrame({
+        "A": ["S", "W", "W"],
+        "B": [1, 1, 2],
+    })
+    res = df.groupby("A").agg(
+        {"B": lambda x: x.get(x.index[-1])}
+    )
+    expected = pd.DataFrame(dict(A=["S", "W"], B=[1.0, 2.0])).set_index("A")
+    pd.testing.assert_frame_equal(res, expected)