Updating sort_index for Series to follow pattern DataFrame

Author: brandonmburroughs

pandas/core/series.py

@@ -1773,7 +1773,7 @@ def _try_kind_sort(arr):
 
     @Appender(generic._shared_docs['sort_index'] % _shared_doc_kwargs)
     def sort_index(self, axis=0, level=None, ascending=True, inplace=False,
-                   sort_remaining=True):
+                   kind='quicksort', na_position='last', sort_remaining=True):
 
         axis = self._get_axis_number(axis)
         index = self.index
@@ -1786,8 +1786,18 @@ def sort_index(self, axis=0, level=None, ascending=True, inplace=False,
             indexer = _ensure_platform_int(indexer)
             new_index = index.take(indexer)
         else:
-            new_index, indexer = index.sort_values(return_indexer=True,
-                                                   ascending=ascending)
+            from pandas.core.groupby import _nargsort
+
+            if ((ascending and index.is_monotonic_increasing) or
+                    (not ascending and index.is_monotonic_decreasing)):
+                if inplace:
+                    return
+                else:
+                    return self.copy()
+
+            indexer = _nargsort(index, kind=kind, ascending=ascending,
+                                na_position=na_position)
+            new_index = index.take(indexer)
 
         new_values = self._values.take(indexer)
         result = self._constructor(new_values, index=new_index)

pandas/tests/series/test_sorting.py

@@ -144,3 +144,27 @@ def test_sort_index_multiindex(self):
         # rows share same level='A': sort has no effect without remaining lvls
         res = s.sort_index(level='A', sort_remaining=False)
         assert_series_equal(s, res)
+
+    def test_sort_index_kind(self):
+        series = Series(index=[3, 2, 1, 4, 3])
+        expected_series = Series(index=[1, 2, 3, 3, 4])
+
+        index_sorted_series = series.sort_index(kind='mergesort')
+        assert_series_equal(expected_series, index_sorted_series)
+
+        index_sorted_series = series.sort_index(kind='quicksort')
+        assert_series_equal(expected_series, index_sorted_series)
+
+        index_sorted_series = series.sort_index(kind='heapsort')
+        assert_series_equal(expected_series, index_sorted_series)
+
+    def test_sort_index_na_position(self):
+        series = Series(index=[3, 2, 1, 4, 3, np.nan])
+
+        expected_series_first = Series(index=[np.nan, 1, 2, 3, 3, 4])
+        index_sorted_series = series.sort_index(na_position='first')
+        assert_series_equal(expected_series_first, index_sorted_series)
+
+        expected_series_last = Series(index=[1, 2, 3, 3, 4, np.nan])
+        index_sorted_series = series.sort_index(na_position='last')
+        assert_series_equal(expected_series_last, index_sorted_series)