Add asv test that exercises code, update docs

Author: erikoveson

asv_bench/benchmarks/categoricals.py

@@ -47,6 +47,7 @@ def setup(self):
         self.values_all_nan = [np.nan] * len(self.values)
         self.values_all_int8 = np.ones(N, 'int8')
         self.categorical = pd.Categorical(self.values, self.categories)
+        self.series = pd.Series(self.categorical)
 
     def time_regular(self):
         pd.Categorical(self.values, self.categories)
@@ -72,6 +73,9 @@ def time_from_codes_all_int8(self):
     def time_existing_categorical(self):
         pd.Categorical(self.categorical)
 
+    def time_existing_series(self):
+        pd.Categorical(self.series)
+
 
 class ValueCounts(object):
 

doc/source/whatsnew/v0.24.0.rst

@@ -1150,7 +1150,7 @@ Performance Improvements
 - Improved performance of :func:`pd.concat` for `Series` objects (:issue:`23404`)
 - Improved performance of :meth:`DatetimeIndex.normalize` and :meth:`Timestamp.normalize` for timezone naive or UTC datetimes (:issue:`23634`)
 - Improved performance of :meth:`DatetimeIndex.tz_localize` and various ``DatetimeIndex`` attributes with dateutil UTC timezone (:issue:`23772`)
-- Improved performance of :meth:`Categorical.__init__` (:issue:`23814`)
+- Improved performance of :class:`Categorical` constructor for `Series` objects (:issue:`23814`)
 
 .. _whatsnew_0240.docs: