googleapis · TrevorBergeron · Oct 17, 2025 · Oct 15, 2025
@@ -2555,25 +2555,33 @@ def sort_index(
    ) -> None:
        ...

-    @validations.requires_index
    def sort_index(
        self,
        *,
+        axis: Union[int, str] = 0,
        ascending: bool = True,
        inplace: bool = False,
        na_position: Literal["first", "last"] = "last",
    ) -> Optional[DataFrame]:
-        if na_position not in ["first", "last"]:
-            raise ValueError("Param na_position must be one of 'first' or 'last'")
-        na_last = na_position == "last"
-        index_columns = self._block.index_columns
-        ordering = [
-            order.ascending_over(column, na_last)
-            if ascending
-            else order.descending_over(column, na_last)
-            for column in index_columns
-        ]
-        block = self._block.order_by(ordering)
+        if utils.get_axis_number(axis) == 0:
+            if na_position not in ["first", "last"]:
+                raise ValueError("Param na_position must be one of 'first' or 'last'")
+            na_last = na_position == "last"
+            index_columns = self._block.index_columns
+            ordering = [
+                order.ascending_over(column, na_last)
+                if ascending
+                else order.descending_over(column, na_last)
+                for column in index_columns
+            ]
+            block = self._block.order_by(ordering)
+        else:  # axis=1
+            _, indexer = self.columns.sort_values(
+                return_indexer=True, ascending=ascending, na_position=na_position  # type: ignore
+            )
+            block = self._block.select_columns(
+                [self._block.value_columns[i] for i in indexer]
+            )
        if inplace:
            self._set_block(block)
            return None

@@ -2406,13 +2406,19 @@ def test_set_index_key_error(scalars_dfs):
    ("na_position",),
    (("first",), ("last",)),
 )
-def test_sort_index(scalars_dfs, ascending, na_position):
+@pytest.mark.parametrize(
+    ("axis",),
+    ((0,), ("columns",)),
+)
+def test_sort_index(scalars_dfs, ascending, na_position, axis):
    index_column = "int64_col"
    scalars_df, scalars_pandas_df = scalars_dfs
    df = scalars_df.set_index(index_column)
-    bf_result = df.sort_index(ascending=ascending, na_position=na_position).to_pandas()
+    bf_result = df.sort_index(
+        ascending=ascending, na_position=na_position, axis=axis
+    ).to_pandas()
    pd_result = scalars_pandas_df.set_index(index_column).sort_index(
-        ascending=ascending, na_position=na_position
+        ascending=ascending, na_position=na_position, axis=axis
    )
    pandas.testing.assert_frame_equal(bf_result, pd_result)


@@ -1757,13 +1757,19 @@ def test_set_index_key_error(scalars_dfs):
    ("na_position",),
    (("first",), ("last",)),
 )
-def test_sort_index(scalars_dfs, ascending, na_position):
+@pytest.mark.parametrize(
+    ("axis",),
+    ((0,), ("columns",)),
+)
+def test_sort_index(scalars_dfs, ascending, na_position, axis):
    index_column = "int64_col"
    scalars_df, scalars_pandas_df = scalars_dfs
    df = scalars_df.set_index(index_column)
-    bf_result = df.sort_index(ascending=ascending, na_position=na_position).to_pandas()
+    bf_result = df.sort_index(
+        ascending=ascending, na_position=na_position, axis=axis
+    ).to_pandas()
    pd_result = scalars_pandas_df.set_index(index_column).sort_index(
-        ascending=ascending, na_position=na_position
+        ascending=ascending, na_position=na_position, axis=axis
    )
    pandas.testing.assert_frame_equal(bf_result, pd_result)


@@ -2382,13 +2382,17 @@ def sort_values(
    def sort_index(
        self,
        *,
+        axis: str | int = 0,
        ascending: bool = True,
        inplace: bool = False,
        na_position: Literal["first", "last"] = "last",
    ):
        """Sort object by labels (along an axis).

        Args:
+            axis ({0 or 'index', 1 or 'columns'}, default 0):
+                The axis along which to sort.  The value 0 identifies the rows,
+                and 1 identifies the columns.
            ascending (bool, default True)
                Sort ascending vs. descending.
            inplace (bool, default False):