From 89880b529065f8324c19bc5dfd78bd488607aebf Mon Sep 17 00:00:00 2001
From: dcherian <deepak@cherian.net>
Date: Mon, 8 May 2023 17:14:18 -0600
Subject: [PATCH 1/3] Fix .groupby(multi index level)

Closes #6836
---
 xarray/core/groupby.py       | 2 +-
 xarray/tests/test_groupby.py | 8 ++++++++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/xarray/core/groupby.py b/xarray/core/groupby.py
index 55fe103d41e..ac21cb03093 100644
--- a/xarray/core/groupby.py
+++ b/xarray/core/groupby.py
@@ -381,7 +381,7 @@ def is_unique_and_monotonic(self) -> bool:
     @property
     def group_as_index(self) -> pd.Index:
         if self._group_as_index is None:
-            self._group_as_index = safe_cast_to_index(self.group1d)
+            self._group_as_index = self.group1d.to_index()
         return self._group_as_index
 
 
diff --git a/xarray/tests/test_groupby.py b/xarray/tests/test_groupby.py
index a8530d85235..13c2c82e3b0 100644
--- a/xarray/tests/test_groupby.py
+++ b/xarray/tests/test_groupby.py
@@ -2336,3 +2336,11 @@ def test_groupby_binary_op_regression() -> None:
     anom_gb = x_slice.groupby("time.month") - clim
 
     assert_identical(xr.zeros_like(anom_gb), anom_gb)
+
+
+def test_groupby_multiindex_level():
+    # GH6836
+    midx = pd.MultiIndex.from_product([list("abc"), [0, 1]], names=("one", "two"))
+    mda = xr.DataArray(np.random.rand(6, 3), [("x", midx), ("y", range(3))])
+    groups = mda.groupby("one").groups
+    assert groups == {"a": [0, 1], "b": [2, 3], "c": [4, 5]}

From 2697cee3b795f6864b5695a79fd83e5d4fb3cc86 Mon Sep 17 00:00:00 2001
From: Illviljan <14371165+Illviljan@users.noreply.github.com>
Date: Fri, 12 May 2023 06:41:43 +0200
Subject: [PATCH 2/3] Update xarray/tests/test_groupby.py

---
 xarray/tests/test_groupby.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xarray/tests/test_groupby.py b/xarray/tests/test_groupby.py
index bacb9d0e104..8a93cf930a5 100644
--- a/xarray/tests/test_groupby.py
+++ b/xarray/tests/test_groupby.py
@@ -2340,7 +2340,7 @@ def test_groupby_binary_op_regression() -> None:
     assert_identical(xr.zeros_like(anom_gb), anom_gb)
 
 
-def test_groupby_multiindex_level():
+def test_groupby_multiindex_level() -> None:
     # GH6836
     midx = pd.MultiIndex.from_product([list("abc"), [0, 1]], names=("one", "two"))
     mda = xr.DataArray(np.random.rand(6, 3), [("x", midx), ("y", range(3))])

From dc7f6383fca6d0ed52c3fd727fe7b16c45bef478 Mon Sep 17 00:00:00 2001
From: dcherian <deepak@cherian.net>
Date: Fri, 12 May 2023 10:11:42 -0600
Subject: [PATCH 3/3] mypy: Add _DummyGroup.to_index

---
 xarray/core/groupby.py | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/xarray/core/groupby.py b/xarray/core/groupby.py
index 1f18396725e..1bda5568c9a 100644
--- a/xarray/core/groupby.py
+++ b/xarray/core/groupby.py
@@ -236,6 +236,10 @@ def __getitem__(self, key):
             key = key[0]
         return self.values[key]
 
+    def to_index(self) -> pd.Index:
+        # could be pd.RangeIndex?
+        return pd.Index(np.arange(self.size))
+
     def copy(self, deep: bool = True, data: Any = None):
         raise NotImplementedError