TST: test that re-using a list of groupers will not throw ValueError

Author: jarent-nvidia

pandas/tests/groupby/test_grouping.py

@@ -875,6 +875,25 @@ def test_groupby_tuple_keys_handle_multiindex(self):
         expected = expected[result.columns]
         tm.assert_frame_equal(result.reset_index(drop=True), expected)
 
+    def test_groupby_grouper_immutable_list_item(self):
+        # GH 26564 - prevent 'ValueError: all keys need to be the same shape' when re-using a list of groupers
+        df1 = pd.DataFrame(
+            [
+                ["05/29/2019"], 
+                ["05/28/2019"]
+            ], 
+            columns=["date"]).assign(date=lambda df: pd.to_datetime(df["date"])
+        )
+        df2 = pd.DataFrame(
+            columns=["date"]).assign(date=lambda df: pd.to_datetime(df["date"])
+        )
+
+        groupers = [pd.Grouper(key="date", freq="1D")]
+
+        df1.groupby(groupers).head()
+        # no error
+        df2.groupby(groupers).head()
+
 
 # get_group
 # --------------------------------