TST: Test for issue #22797

Testing return order of MultiIndex.loc

MultiIndex.loc try to return the result in the same order as the key
given.

Author: nrebena

pandas/tests/indexes/multi/test_indexing.py

@@ -437,3 +437,21 @@ def test_timestamp_multiindex_indexer():
     )
     should_be = pd.Series(data=np.arange(24, len(qidx) + 24), index=qidx, name="foo")
     tm.assert_series_equal(result, should_be)
+
+
+def test_multiindex_loc_order():
+    # GH 22797
+    # Try to respect order of keys given for MultiIndex.loc
+    df = pd.DataFrame(
+        np.arange(12).reshape((4, 3)),
+        index=[["a", "a", "b", "b"], [1, 2, 1, 2]],
+        columns=[["Ohio", "Ohio", "Colorado"], ["Green", "Red", "Green"]],
+    )
+
+    res = df.loc[["b", "a"], :]
+    exp_index = pd.MultiIndex.from_arrays([["b", "b", "a", "a"], [1, 2, 1, 2]])
+    tm.assert_index_equal(res.index, exp_index)
+
+    res = df.loc[(["b", "a"], [2, 1]), :]
+    exp_index = pd.MultiIndex.from_arrays([["b", "b", "a", "a"], [2, 1, 2, 1]])
+    tm.assert_index_equal(res.index, exp_index)