imroved performance of CategoricalIndex.is_monotonic*

Author: tp

doc/source/whatsnew/v0.23.0.txt

@@ -1079,6 +1079,7 @@ Performance Improvements
 - Improved performance of :func:`pandas.core.groupby.GroupBy.pct_change` (:issue:`19165`)
 - Improved performance of :func:`Series.isin` in the case of categorical dtypes (:issue:`20003`)
 - Improved performance of ``getattr(Series, attr)`` when the Series has certain index types. This manifiested in slow printing of large Series with a ``DatetimeIndex`` (:issue:`19764`)
+- Improved performance of :meth:`CategoricalIndex.is_monotonic_increasing`, :meth:`CategoricalIndex.is_monotonic_decreasing` and :meth:`CategoricalIndex.is_monotonic` (:issue:`21025`)
 - Fixed a performance regression for :func:`GroupBy.nth` and :func:`GroupBy.last` with some object columns (:issue:`19283`)
 
 .. _whatsnew_0230.docs:

pandas/core/indexes/category.py

@@ -382,11 +382,11 @@ def is_unique(self):
 
     @property
     def is_monotonic_increasing(self):
-        return Index(self.codes).is_monotonic_increasing
+        return self._engine.is_monotonic_increasing
 
     @property
     def is_monotonic_decreasing(self):
-        return Index(self.codes).is_monotonic_decreasing
+        return self._engine.is_monotonic_decreasing
 
     @Appender(_index_shared_docs['index_unique'] % _index_doc_kwargs)
     def unique(self, level=None):