BUG: Attributes are lost when subsetting columns

Author: rhshadrach

pandas/core/groupby/generic.py

@@ -1662,11 +1662,18 @@ def _gotitem(self, key, ndim: int, subset=None):
             return DataFrameGroupBy(
                 subset,
                 self.grouper,
-                selection=key,
+                axis=self.axis,
+                level=self.level,
                 grouper=self.grouper,
                 exclusions=self.exclusions,
+                selection=key,
                 as_index=self.as_index,
+                sort=self.sort,
+                group_keys=self.group_keys,
+                squeeze=self.squeeze,
                 observed=self.observed,
+                mutated=self.mutated,
+                dropna=self.dropna,
             )
         elif ndim == 1:
             if subset is None:

pandas/tests/groupby/test_groupby.py

@@ -2055,3 +2055,27 @@ def test_groups_repr_truncates(max_seq_items, expected):
 
         result = df.groupby(np.array(df.a)).groups.__repr__()
         assert result == expected
+
+
+@pytest.mark.parametrize(
+    "attr, value",
+    [
+        ("axis", 1),
+        ("level", "a"),
+        ("as_index", False),
+        ("sort", False),
+        ("group_keys", False),
+        ("squeeze", True),
+        ("observed", True),
+        ("dropna", False),
+    ],
+)
+def test_subsetting_columns_keeps_attrs(attr, value):
+    # GH 9959 - When subsetting columns, don't drop attributes
+    df = pd.DataFrame({"a": [1], "b": [2], "c": [3]})
+    if attr != "axis":
+        df = df.set_index("a")
+    expected = df.groupby("a", **{attr: value})
+
+    result = expected[["b"]]
+    assert getattr(result, attr) == getattr(expected, attr)