ENH: Add ignore_index to sort_index

doc/source/whatsnew/v1.0.0.rst

@@ -221,6 +221,7 @@ Other enhancements
 - DataFrame constructor preserve `ExtensionArray` dtype with `ExtensionArray` (:issue:`11363`)
 - :meth:`DataFrame.sort_values` and :meth:`Series.sort_values` have gained ``ignore_index`` keyword to be able to reset index after sorting (:issue:`30114`)
 - :meth:`DataFrame.to_markdown` and :meth:`Series.to_markdown` added (:issue:`11052`)
+- :meth:`DataFrame.sort_index` and :meth:`Series.sort_index` have gained ``ignore_index`` keyword to reset index (:issue:`30114`)
 - :meth:`DataFrame.drop_duplicates` has gained ``ignore_index`` keyword to reset index (:issue:`30114`)
 - Added new writer for exporting Stata dta files in version 118, ``StataWriter118``.  This format supports exporting strings containing Unicode characters (:issue:`23573`)
 

pandas/core/frame.py

@@ -1988,7 +1988,7 @@ def to_feather(self, path):
     @Substitution(klass="DataFrame")
     @Appender(_shared_docs["to_markdown"])
     def to_markdown(
-        self, buf: Optional[IO[str]] = None, mode: Optional[str] = None, **kwargs,
+        self, buf: Optional[IO[str]] = None, mode: Optional[str] = None, **kwargs
     ) -> Optional[str]:
         kwargs.setdefault("headers", "keys")
         kwargs.setdefault("tablefmt", "pipe")
@@ -4831,6 +4831,7 @@ def sort_index(
         kind="quicksort",
         na_position="last",
         sort_remaining=True,
+        ignore_index: bool = False,
     ):
 
         # TODO: this can be combined with Series.sort_index impl as
@@ -4881,6 +4882,9 @@ def sort_index(
         # reconstruct axis if needed
         new_data.axes[baxis] = new_data.axes[baxis]._sort_levels_monotonic()
 
+        if ignore_index:
+            new_data.axes[1] = ibase.default_index(len(indexer))
+
         if inplace:
             return self._update_inplace(new_data)
         else:

pandas/core/generic.py

@@ -4178,6 +4178,7 @@ def sort_index(
         kind: str = "quicksort",
         na_position: str = "last",
         sort_remaining: bool_t = True,
+        ignore_index: bool_t = False,
     ):
         """
         Sort object by labels (along an axis).
@@ -4204,6 +4205,10 @@ def sort_index(
         sort_remaining : bool, default True
             If True and sorting by level and index is multilevel, sort by other
             levels too (in order) after sorting by specified level.
+        ignore_index : bool, default False
+            If True, the resulting axis will be labeled 0, 1, …, n - 1.
+
+            .. versionadded:: 1.0.0
 
         Returns
         -------

pandas/core/series.py

@@ -1433,7 +1433,7 @@ def to_string(
     @Substitution(klass="Series")
     @Appender(generic._shared_docs["to_markdown"])
     def to_markdown(
-        self, buf: Optional[IO[str]] = None, mode: Optional[str] = None, **kwargs,
+        self, buf: Optional[IO[str]] = None, mode: Optional[str] = None, **kwargs
     ) -> Optional[str]:
         return self.to_frame().to_markdown(buf, mode, **kwargs)
 
@@ -2963,6 +2963,7 @@ def sort_index(
         kind="quicksort",
         na_position="last",
         sort_remaining=True,
+        ignore_index: bool = False,
     ):
         """
         Sort Series by index labels.
@@ -2991,6 +2992,10 @@ def sort_index(
         sort_remaining : bool, default True
             If True and sorting by level and index is multilevel, sort by other
             levels too (in order) after sorting by specified level.
+        ignore_index : bool, default False
+            If True, the resulting axis will be labeled 0, 1, …, n - 1.
+
+            .. versionadded:: 1.0.0
 
         Returns
         -------
@@ -3118,6 +3123,9 @@ def sort_index(
         new_values = self._values.take(indexer)
         result = self._constructor(new_values, index=new_index)
 
+        if ignore_index:
+            result.index = ibase.default_index(len(result))
+
         if inplace:
             self._update_inplace(result)
         else:
@@ -4478,9 +4486,7 @@ def to_period(self, freq=None, copy=True):
     hist = pandas.plotting.hist_series
 
 
-Series._setup_axes(
-    ["index"], docs={"index": "The index (axis labels) of the Series."},
-)
+Series._setup_axes(["index"], docs={"index": "The index (axis labels) of the Series."})
 Series._add_numeric_operations()
 Series._add_series_or_dataframe_operations()
 

pandas/tests/frame/methods/test_sort_index.py

@@ -229,3 +229,85 @@ def test_sort_index_intervalindex(self):
         )
         result = result.columns.levels[1].categories
         tm.assert_index_equal(result, expected)
+
+    @pytest.mark.parametrize(
+        "original_dict, sorted_dict, ascending, ignore_index, output_index",
+        [
+            ({"A": [1, 2, 3]}, {"A": [2, 3, 1]}, False, True, [0, 1, 2]),
+            ({"A": [1, 2, 3]}, {"A": [1, 3, 2]}, True, True, [0, 1, 2]),
+            ({"A": [1, 2, 3]}, {"A": [2, 3, 1]}, False, False, [5, 3, 2]),
+            ({"A": [1, 2, 3]}, {"A": [1, 3, 2]}, True, False, [2, 3, 5]),
+        ],
+    )
+    def test_sort_index_ignore_index(
+        self, original_dict, sorted_dict, ascending, ignore_index, output_index
+    ):
+        # GH 30114
+        original_index = [2, 5, 3]
+        df = DataFrame(original_dict, index=original_index)
+        expected_df = DataFrame(sorted_dict, index=output_index)
+
+        sorted_df = df.sort_index(ascending=ascending, ignore_index=ignore_index)
+        tm.assert_frame_equal(sorted_df, expected_df)
+        tm.assert_frame_equal(df, DataFrame(original_dict, index=original_index))
+
+        # Test when inplace is True
+        copied_df = df.copy()
+        copied_df.sort_index(
+            ascending=ascending, ignore_index=ignore_index, inplace=True
+        )
+        tm.assert_frame_equal(copied_df, expected_df)
+        tm.assert_frame_equal(df, DataFrame(original_dict, index=original_index))
+
+    @pytest.mark.parametrize(
+        "original_dict, sorted_dict, ascending, ignore_index, output_index",
+        [
+            (
+                {"M1": [1, 2], "M2": [3, 4]},
+                {"M1": [1, 2], "M2": [3, 4]},
+                True,
+                True,
+                [0, 1],
+            ),
+            (
+                {"M1": [1, 2], "M2": [3, 4]},
+                {"M1": [2, 1], "M2": [4, 3]},
+                False,
+                True,
+                [0, 1],
+            ),
+            (
+                {"M1": [1, 2], "M2": [3, 4]},
+                {"M1": [1, 2], "M2": [3, 4]},
+                True,
+                False,
+                MultiIndex.from_tuples([[2, 1], [3, 4]], names=list("AB")),
+            ),
+            (
+                {"M1": [1, 2], "M2": [3, 4]},
+                {"M1": [2, 1], "M2": [4, 3]},
+                False,
+                False,
+                MultiIndex.from_tuples([[3, 4], [2, 1]], names=list("AB")),
+            ),
+        ],
+    )
+    def test_sort_index_ignore_index_multi_index(
+        self, original_dict, sorted_dict, ascending, ignore_index, output_index
+    ):
+        # GH 30114, this is to test ignore_index on MulitIndex of index
+        mi = MultiIndex.from_tuples([[2, 1], [3, 4]], names=list("AB"))
+        df = DataFrame(original_dict, index=mi)
+        expected_df = DataFrame(sorted_dict, index=output_index)
+
+        sorted_df = df.sort_index(ascending=ascending, ignore_index=ignore_index)
+        tm.assert_frame_equal(sorted_df, expected_df)
+        tm.assert_frame_equal(df, DataFrame(original_dict, index=mi))
+
+        # Test when inplace is True
+        copied_df = df.copy()
+        copied_df.sort_index(
+            ascending=ascending, ignore_index=ignore_index, inplace=True
+        )
+        tm.assert_frame_equal(copied_df, expected_df)
+        tm.assert_frame_equal(df, DataFrame(original_dict, index=mi))

pandas/tests/series/methods/test_sort_index.py

@@ -135,3 +135,34 @@ def test_sort_index_intervals(self):
             [3, 2, 1, np.nan], IntervalIndex.from_arrays([3, 2, 1, 0], [4, 3, 2, 1])
         )
         tm.assert_series_equal(result, expected)
+
+    @pytest.mark.parametrize(
+        "original_list, sorted_list, ascending, ignore_index, output_index",
+        [
+            ([2, 3, 6, 1], [2, 3, 6, 1], True, True, [0, 1, 2, 3]),
+            ([2, 3, 6, 1], [2, 3, 6, 1], True, False, [0, 1, 2, 3]),
+            ([2, 3, 6, 1], [1, 6, 3, 2], False, True, [0, 1, 2, 3]),
+            ([2, 3, 6, 1], [1, 6, 3, 2], False, False, [3, 2, 1, 0]),
+        ],
+    )
+    def test_sort_index_ignore_index(
+        self, original_list, sorted_list, ascending, ignore_index, output_index
+    ):
+        # GH 30114
+        ser = Series(original_list)
+        expected = Series(sorted_list, index=output_index)
+
+        # Test when inplace is False
+        sorted_sr = ser.sort_index(ascending=ascending, ignore_index=ignore_index)
+        tm.assert_series_equal(sorted_sr, expected)
+
+        tm.assert_series_equal(ser, Series(original_list))
+
+        # Test when inplace is True
+        copied_sr = ser.copy()
+        copied_sr.sort_index(
+            ascending=ascending, ignore_index=ignore_index, inplace=True
+        )
+        tm.assert_series_equal(copied_sr, expected)
+
+        tm.assert_series_equal(ser, Series(original_list))