ENH: Implement PeriodIndex.intersection without object-dtype cast (#30666)

Author: jbrockmendel

pandas/core/indexes/base.py

@@ -2408,14 +2408,8 @@ def intersection(self, other, sort=False):
  return this.intersection(other, sort=sort)
 
  # TODO(EA): setops-refactor, clean all this up
- if is_period_dtype(self):
- lvals = self._ndarray_values
- else:
- lvals = self._values
- if is_period_dtype(other):
- rvals = other._ndarray_values
- else:
- rvals = other._values
+ lvals = self._values
+ rvals = other._values
 
  if self.is_monotonic and other.is_monotonic:
  try:
@@ -2434,18 +2428,13 @@ def intersection(self, other, sort=False):
  indexer = indexer[indexer != -1]
 
  taken = other.take(indexer)
+ res_name = get_op_result_name(self, other)
 
  if sort is None:
  taken = algos.safe_sort(taken.values)
- if self.name != other.name:
- name = None
- else:
- name = self.name
- return self._shallow_copy(taken, name=name)
-
- if self.name != other.name:
- taken.name = None
+ return self._shallow_copy(taken, name=res_name)
 
+ taken.name = res_name
  return taken
 
  def difference(self, other, sort=None):

pandas/core/indexes/datetimelike.py

@@ -721,12 +721,9 @@ def intersection(self, other, sort=False):
  # this point, depending on the values.
 
  result._set_freq(None)
- if hasattr(self, "tz"):
- result = self._shallow_copy(
- result._values, name=result.name, tz=result.tz, freq=None
- )
- else:
- result = self._shallow_copy(result._values, name=result.name, freq=None)
+ result = self._shallow_copy(
+ result._data, name=result.name, dtype=result.dtype, freq=None
+ )
  if result.freq is None:
  result._set_freq("infer")
  return result

pandas/core/indexes/period.py

@@ -12,6 +12,7 @@
  ensure_platform_int,
  is_bool_dtype,
  is_datetime64_any_dtype,
+ is_dtype_equal,
  is_float,
  is_float_dtype,
  is_integer,
@@ -782,6 +783,9 @@ def join(self, other, how="left", level=None, return_indexers=False, sort=False)
  return self._apply_meta(result), lidx, ridx
  return self._apply_meta(result)
 
+ # ------------------------------------------------------------------------
+ # Set Operation Methods
+
  def _assert_can_do_setop(self, other):
  super()._assert_can_do_setop(other)
 
@@ -799,6 +803,30 @@ def _wrap_setop_result(self, other, result):
  result.name = name
  return result
 
+ def intersection(self, other, sort=False):
+ self._validate_sort_keyword(sort)
+ self._assert_can_do_setop(other)
+ res_name = get_op_result_name(self, other)
+ other = ensure_index(other)
+
+ if self.equals(other):
+ return self._get_reconciled_name_object(other)
+
+ if not is_dtype_equal(self.dtype, other.dtype):
+ # TODO: fastpath for if we have a different PeriodDtype
+ this = self.astype("O")
+ other = other.astype("O")
+ return this.intersection(other, sort=sort)
+
+ i8self = Int64Index._simple_new(self.asi8)
+ i8other = Int64Index._simple_new(other.asi8)
+ i8result = i8self.intersection(i8other, sort=sort)
+
+ result = self._shallow_copy(np.asarray(i8result, dtype=np.int64), name=res_name)
+ return result
+
+ # ------------------------------------------------------------------------
+
  def _apply_meta(self, rawarr):
  if not isinstance(rawarr, PeriodIndex):
  rawarr = PeriodIndex._simple_new(rawarr, freq=self.freq, name=self.name)