PERF: scalar not found in categorical's categories

Author: topper-123

doc/source/whatsnew/v1.0.0.rst

@@ -343,6 +343,7 @@ Performance improvements
 - 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`)
+- Performance improvement when searching for a scalar in a :meth:`Categorical` and the scalar is not found in the categories (:issue:`29750`)
 
 .. _whatsnew_1000.bug_fixes:
 

pandas/core/arrays/categorical.py

@@ -133,9 +133,9 @@ def f(self, other):
                 return ret
             else:
                 if opname == "__eq__":
-                    return np.repeat(False, len(self))
+                    return np.zeros(len(self), dtype=bool)
                 elif opname == "__ne__":
-                    return np.repeat(True, len(self))
+                    return np.ones(len(self), dtype=bool)
                 else:
                     msg = (
                         "Cannot compare a Categorical for op {op} with a "