ENH: use stable sort in value_counts

pandas/core/algorithms.py

@@ -948,7 +948,7 @@ def value_counts_internal(
             result = Series(counts, index=idx, name=name, copy=False)
 
     if sort:
-        result = result.sort_values(ascending=ascending)
+        result = result.sort_values(ascending=ascending, kind="stable")
 
     if normalize:
         result = result / counts.sum()

pandas/core/base.py

@@ -993,7 +993,12 @@ def value_counts(
             If True then the object returned will contain the relative
             frequencies of the unique values.
         sort : bool, default True
-            Sort by frequencies when True. Preserve the order of the data when False.
+            Stable sort by frequencies when True. Preserve the order of the data
+            when False.
+
+            .. versionchanged:: 3.0.0
+
+                Prior to 3.0.0, the sort was unstable.
         ascending : bool, default False
             Sort in ascending order.
         bins : int, optional

pandas/core/frame.py

@@ -7718,11 +7718,16 @@ def value_counts(
         normalize : bool, default False
             Return proportions rather than frequencies.
         sort : bool, default True
-            Sort by frequencies when True. Preserve the order of the data when False.
+            Stable sort by frequencies when True. Preserve the order of the data
+            when False.
 
             .. versionchanged:: 3.0.0
 
                 Prior to 3.0.0, ``sort=False`` would sort by the columns values.
+
+            .. versionchanged:: 3.0.0
+
+                Prior to 3.0.0, the sort was unstable.
         ascending : bool, default False
             Sort in ascending order.
         dropna : bool, default True
@@ -7832,7 +7837,7 @@ def value_counts(
         counts.name = name
 
         if sort:
-            counts = counts.sort_values(ascending=ascending)
+            counts = counts.sort_values(ascending=ascending, kind="stable")
         if normalize:
             counts /= counts.sum()
 

pandas/core/groupby/generic.py

@@ -2776,8 +2776,8 @@ def value_counts(
         normalize : bool, default False
             Return proportions rather than frequencies.
         sort : bool, default True
-            Sort by frequencies when True. When False, non-grouping columns will appear
-            in the order they occur in within groups.
+            Stable sort by frequencies when True. When False, non-grouping
+            columns will appear in the order they occur in within groups.
 
             .. versionchanged:: 3.0.0