REF: de-duplicate IntervalIndex setops (#41832)

Author: jbrockmendel

pandas/core/indexes/base.py

@@ -3013,7 +3013,7 @@ def _union(self, other: Index, sort):
 
         # Self may have duplicates
         # find indexes of things in "other" that are not in "self"
-        if self.is_unique:
+        if self._index_as_unique:
             indexer = self.get_indexer(other)
             missing = (indexer == -1).nonzero()[0]
         else:
@@ -3171,14 +3171,18 @@ def difference(self, other, sort=None):
             # Note: we do not (yet) sort even if sort=None GH#24959
             return self.rename(result_name)
 
+        if not self._should_compare(other):
+            # Nothing matches -> difference is everything
+            return self.rename(result_name)
+
         result = self._difference(other, sort=sort)
         return self._wrap_setop_result(other, result)
 
     def _difference(self, other, sort):
 
         this = self._get_unique_index()
 
-        indexer = this.get_indexer(other)
+        indexer = this.get_indexer_for(other)
         indexer = indexer.take((indexer != -1).nonzero()[0])
 
         label_diff = np.setdiff1d(np.arange(this.size), indexer, assume_unique=True)

pandas/core/indexes/interval.py

@@ -1,7 +1,6 @@
 """ define the IntervalIndex """
 from __future__ import annotations
 
-from functools import wraps
 from operator import (
     le,
     lt,
@@ -63,10 +62,7 @@
 )
 from pandas.core.dtypes.dtypes import IntervalDtype
 
-from pandas.core.algorithms import (
-    take_nd,
-    unique,
-)
+from pandas.core.algorithms import take_nd
 from pandas.core.arrays.interval import (
     IntervalArray,
     _interval_shared_docs,
@@ -93,7 +89,6 @@
     TimedeltaIndex,
     timedelta_range,
 )
-from pandas.core.ops import get_op_result_name
 
 if TYPE_CHECKING:
     from pandas import CategoricalIndex
@@ -151,59 +146,6 @@ def _new_IntervalIndex(cls, d):
     return cls.from_arrays(**d)
 
 
-def setop_check(method):
-    """
-    This is called to decorate the set operations of IntervalIndex
-    to perform the type check in advance.
-    """
-    op_name = method.__name__
-
-    @wraps(method)
-    def wrapped(self, other, sort=False):
-        self._validate_sort_keyword(sort)
-        self._assert_can_do_setop(other)
-        other, result_name = self._convert_can_do_setop(other)
-
-        if op_name == "difference":
-            if not isinstance(other, IntervalIndex):
-                result = getattr(self.astype(object), op_name)(other, sort=sort)
-                return result.astype(self.dtype)
-
-            elif not self._should_compare(other):
-                # GH#19016: ensure set op will not return a prohibited dtype
-                result = getattr(self.astype(object), op_name)(other, sort=sort)
-                return result.astype(self.dtype)
-
-        return method(self, other, sort)
-
-    return wrapped
-
-
-def _setop(op_name: str):
-    """
-    Implement set operation.
-    """
-
-    def func(self, other, sort=None):
-        # At this point we are assured
-        #  isinstance(other, IntervalIndex)
-        #  other.closed == self.closed
-
-        result = getattr(self._multiindex, op_name)(other._multiindex, sort=sort)
-        result_name = get_op_result_name(self, other)
-
-        # GH 19101: ensure empty results have correct dtype
-        if result.empty:
-            result = result._values.astype(self.dtype.subtype)
-        else:
-            result = result._values
-
-        return type(self).from_tuples(result, closed=self.closed, name=result_name)
-
-    func.__name__ = op_name
-    return setop_check(func)
-
-
 @Appender(
     _interval_shared_docs["class"]
     % {
@@ -859,11 +801,11 @@ def _intersection(self, other, sort):
         """
         # For IntervalIndex we also know other.closed == self.closed
         if self.left.is_unique and self.right.is_unique:
-            taken = self._intersection_unique(other)
+            return super()._intersection(other, sort=sort)
         elif other.left.is_unique and other.right.is_unique and self.isna().sum() <= 1:
             # Swap other/self if other is unique and self does not have
             # multiple NaNs
-            taken = other._intersection_unique(self)
+            return super()._intersection(other, sort=sort)
         else:
             # duplicates
             taken = self._intersection_non_unique(other)
@@ -873,29 +815,6 @@ def _intersection(self, other, sort):
 
         return taken
 
-    def _intersection_unique(self, other: IntervalIndex) -> IntervalIndex:
-        """
-        Used when the IntervalIndex does not have any common endpoint,
-        no matter left or right.
-        Return the intersection with another IntervalIndex.
-
-        Parameters
-        ----------
-        other : IntervalIndex
-
-        Returns
-        -------
-        IntervalIndex
-        """
-        lindexer = self.left.get_indexer(other.left)
-        rindexer = self.right.get_indexer(other.right)
-
-        match = (lindexer == rindexer) & (lindexer != -1)
-        indexer = lindexer.take(match.nonzero()[0])
-        indexer = unique(indexer)
-
-        return self.take(indexer)
-
     def _intersection_non_unique(self, other: IntervalIndex) -> IntervalIndex:
         """
         Used when the IntervalIndex does have some common endpoints,
@@ -923,9 +842,6 @@ def _intersection_non_unique(self, other: IntervalIndex) -> IntervalIndex:
 
         return self[mask]
 
-    _union = _setop("union")
-    _difference = _setop("difference")
-
     # --------------------------------------------------------------------
 
     @property