Backport PR #54641 on branch 2.1.x (BUG: getitem indexing wrong axis) (#54669)

Backport PR #54641: BUG: getitem indexing wrong axis

Co-authored-by: Patrick Hoefler <[email protected]>

Author: meeseeksmachine

pandas/core/indexing.py

@@ -985,8 +985,9 @@ def _getitem_tuple_same_dim(self, tup: tuple):
         """
         retval = self.obj
         # Selecting columns before rows is signficiantly faster
+        start_val = (self.ndim - len(tup)) + 1
         for i, key in enumerate(reversed(tup)):
-            i = self.ndim - i - 1
+            i = self.ndim - i - start_val
             if com.is_null_slice(key):
                 continue
 

pandas/tests/frame/indexing/test_getitem.py

@@ -458,6 +458,14 @@ def test_getitem_datetime_slice(self):
         ):
             df["2011-01-01":"2011-11-01"]
 
+    def test_getitem_slice_same_dim_only_one_axis(self):
+        # GH#54622
+        df = DataFrame(np.random.default_rng(2).standard_normal((10, 8)))
+        result = df.iloc[(slice(None, None, 2),)]
+        assert result.shape == (5, 8)
+        expected = df.iloc[slice(None, None, 2), slice(None)]
+        tm.assert_frame_equal(result, expected)
+
 
 class TestGetitemDeprecatedIndexers:
     @pytest.mark.parametrize("key", [{"a", "b"}, {"a": "a"}])