PERF: improve perf. of Categorical.searchsorted (pandas-dev#28795)

Author: topper-123

asv_bench/benchmarks/categoricals.py

@@ -282,4 +282,18 @@ def time_sort_values(self):
         self.index.sort_values(ascending=False)
 
 
+class SearchSorted:
+    def setup(self):
+        N = 10 ** 5
+        self.ci = tm.makeCategoricalIndex(N).sort_values()
+        self.c = self.ci.values
+        self.key = self.ci.categories[1]
+
+    def time_categorical_index_contains(self):
+        self.ci.searchsorted(self.key)
+
+    def time_categorical_contains(self):
+        self.c.searchsorted(self.key)
+
+
 from .pandas_vb_common import setup  # noqa: F401 isort:skip

doc/source/whatsnew/v1.0.0.rst

@@ -204,6 +204,7 @@ Performance improvements
 - Performance improvement in :meth:`DataFrame.corr` when ``method`` is ``"spearman"`` (:issue:`28139`)
 - Performance improvement in :meth:`DataFrame.replace` when provided a list of values to replace (:issue:`28099`)
 - Performance improvement in :meth:`DataFrame.select_dtypes` by using vectorization instead of iterating over a loop (:issue:`28317`)
+- Performance improvement in :meth:`Categorical.searchsorted` and  :meth:`CategoricalIndex.searchsorted` (:issue:`28795`)
 
 .. _whatsnew_1000.bug_fixes:
 

pandas/core/arrays/categorical.py

@@ -1399,14 +1399,14 @@ def memory_usage(self, deep=False):
     @Substitution(klass="Categorical")
     @Appender(_shared_docs["searchsorted"])
     def searchsorted(self, value, side="left", sorter=None):
-        from pandas.core.series import Series
-
-        codes = _get_codes_for_values(Series(value).values, self.categories)
-        if -1 in codes:
-            raise KeyError("Value(s) to be inserted must be in categories.")
-
-        codes = codes[0] if is_scalar(value) else codes
-
+        # searchsorted is very performance sensitive. By converting codes
+        # to same dtype as self.codes, we get much faster performance.
+        if is_scalar(value):
+            codes = self.categories.get_loc(value)
+            codes = self.codes.dtype.type(codes)
+        else:
+            locs = [self.categories.get_loc(x) for x in value]
+            codes = np.array(locs, dtype=self.codes.dtype)
         return self.codes.searchsorted(codes, side=side, sorter=sorter)
 
     def isna(self):

pandas/core/indexes/category.py

@@ -10,7 +10,7 @@
 from pandas._libs.hashtable import duplicated_int64
 import pandas.compat as compat
 from pandas.compat.numpy import function as nv
-from pandas.util._decorators import Appender, cache_readonly
+from pandas.util._decorators import Appender, Substitution, cache_readonly
 
 from pandas.core.dtypes.common import (
     ensure_platform_int,
@@ -27,6 +27,7 @@
 from pandas.core import accessor
 from pandas.core.algorithms import take_1d
 from pandas.core.arrays.categorical import Categorical, _recode_for_categories, contains
+from pandas.core.base import _shared_docs
 import pandas.core.common as com
 import pandas.core.indexes.base as ibase
 from pandas.core.indexes.base import Index, _index_shared_docs
@@ -555,6 +556,11 @@ def _can_reindex(self, indexer):
         """ always allow reindexing """
         pass
 
+    @Substitution(klass="CategoricalIndex")
+    @Appender(_shared_docs["searchsorted"])
+    def searchsorted(self, value, side="left", sorter=None):
+        return self._data.searchsorted(value, side=side, sorter=sorter)
+
     @Appender(_index_shared_docs["where"])
     def where(self, cond, other=None):
         # TODO: Investigate an alternative implementation with

pandas/tests/arrays/categorical/test_analytics.py

@@ -113,16 +113,15 @@ def test_searchsorted(self, ordered_fixture):
         tm.assert_numpy_array_equal(res_ser, exp)
 
         # Searching for a single value that is not from the Categorical
-        msg = r"Value\(s\) to be inserted must be in categories"
-        with pytest.raises(KeyError, match=msg):
+        with pytest.raises(KeyError, match="cucumber"):
             cat.searchsorted("cucumber")
-        with pytest.raises(KeyError, match=msg):
+        with pytest.raises(KeyError, match="cucumber"):
             ser.searchsorted("cucumber")
 
         # Searching for multiple values one of each is not from the Categorical
-        with pytest.raises(KeyError, match=msg):
+        with pytest.raises(KeyError, match="cucumber"):
             cat.searchsorted(["bread", "cucumber"])
-        with pytest.raises(KeyError, match=msg):
+        with pytest.raises(KeyError, match="cucumber"):
             ser.searchsorted(["bread", "cucumber"])
 
     def test_unique(self):