PERF: perform a unique intersection with IntervalIndex if at least one side is unique

Author: qwhelan

pandas/core/indexes/interval.py

@@ -1143,6 +1143,8 @@ def overlaps(self, other):
     def intersection(self, other, sort=False):
         if self.left.is_unique and self.right.is_unique:
             taken = self._intersection_unique(other)
+        elif other.left.is_unique and other.right.is_unique:
+            taken = other._intersection_unique(self)
         else:
             # duplicates
             taken = self._intersection_non_unique(other)