REF: share IntervalIndex.intersection with Index.intersection (pandas-dev#38373)

Author: jbrockmendel

pandas/core/dtypes/dtypes.py

@@ -1171,3 +1171,15 @@ def __from_arrow__(
             results.append(iarr)
 
         return IntervalArray._concat_same_type(results)
+
+    def _get_common_dtype(self, dtypes: List[DtypeObj]) -> Optional[DtypeObj]:
+        # NB: this doesn't handle checking for closed match
+        if not all(isinstance(x, IntervalDtype) for x in dtypes):
+            return np.dtype(object)
+
+        from pandas.core.dtypes.cast import find_common_type
+
+        common = find_common_type([cast("IntervalDtype", x).subtype for x in dtypes])
+        if common == object:
+            return np.dtype(object)
+        return IntervalDtype(common)

pandas/core/indexes/interval.py

@@ -789,9 +789,11 @@ def _is_comparable_dtype(self, dtype: DtypeObj) -> bool:
         return not is_object_dtype(common_subtype)
 
     def _should_compare(self, other) -> bool:
-        if not super()._should_compare(other):
-            return False
         other = unpack_nested_dtype(other)
+        if is_object_dtype(other.dtype):
+            return True
+        if not self._is_comparable_dtype(other.dtype):
+            return False
         return other.closed == self.closed
 
     # TODO: use should_compare and get rid of _is_non_comparable_own_type
@@ -951,23 +953,6 @@ def _assert_can_do_setop(self, other):
                 "and have compatible dtypes"
             )
 
-    @Appender(Index.intersection.__doc__)
-    def intersection(self, other, sort=False) -> Index:
-        self._validate_sort_keyword(sort)
-        self._assert_can_do_setop(other)
-        other, _ = self._convert_can_do_setop(other)
-
-        if self.equals(other):
-            if self.has_duplicates:
-                return self.unique()._get_reconciled_name_object(other)
-            return self._get_reconciled_name_object(other)
-
-        if not isinstance(other, IntervalIndex):
-            return self.astype(object).intersection(other)
-
-        result = self._intersection(other, sort=sort)
-        return self._wrap_setop_result(other, result)
-
     def _intersection(self, other, sort):
         """
         intersection specialized to the case with matching dtypes.

pandas/tests/dtypes/cast/test_find_common_type.py

@@ -2,7 +2,12 @@
 import pytest
 
 from pandas.core.dtypes.cast import find_common_type
-from pandas.core.dtypes.dtypes import CategoricalDtype, DatetimeTZDtype, PeriodDtype
+from pandas.core.dtypes.dtypes import (
+    CategoricalDtype,
+    DatetimeTZDtype,
+    IntervalDtype,
+    PeriodDtype,
+)
 
 
 @pytest.mark.parametrize(
@@ -120,3 +125,34 @@ def test_period_dtype_mismatch(dtype2):
     dtype = PeriodDtype(freq="D")
     assert find_common_type([dtype, dtype2]) == object
     assert find_common_type([dtype2, dtype]) == object
+
+
+interval_dtypes = [
+    IntervalDtype(np.int64),
+    IntervalDtype(np.float64),
+    IntervalDtype(np.uint64),
+    IntervalDtype(DatetimeTZDtype(unit="ns", tz="US/Eastern")),
+    IntervalDtype("M8[ns]"),
+    IntervalDtype("m8[ns]"),
+]
+
+
+@pytest.mark.parametrize("left", interval_dtypes)
+@pytest.mark.parametrize("right", interval_dtypes)
+def test_interval_dtype(left, right):
+    result = find_common_type([left, right])
+
+    if left is right:
+        assert result is left
+
+    elif left.subtype.kind in ["i", "u", "f"]:
+        # i.e. numeric
+        if right.subtype.kind in ["i", "u", "f"]:
+            # both numeric -> common numeric subtype
+            expected = IntervalDtype(np.float64)
+            assert result == expected
+        else:
+            assert result == object
+
+    else:
+        assert result == object

pandas/tests/indexes/interval/test_setops.py

@@ -61,17 +61,6 @@ def test_intersection(self, closed, sort):
 
         tm.assert_index_equal(index.intersection(index, sort=sort), index)
 
-        # GH 19101: empty result, same dtype
-        other = monotonic_index(300, 314, closed=closed)
-        expected = empty_index(dtype="int64", closed=closed)
-        result = index.intersection(other, sort=sort)
-        tm.assert_index_equal(result, expected)
-
-        # GH 19101: empty result, different dtypes
-        other = monotonic_index(300, 314, dtype="float64", closed=closed)
-        result = index.intersection(other, sort=sort)
-        tm.assert_index_equal(result, expected)
-
         # GH 26225: nested intervals
         index = IntervalIndex.from_tuples([(1, 2), (1, 3), (1, 4), (0, 2)])
         other = IntervalIndex.from_tuples([(1, 2), (1, 3)])
@@ -100,6 +89,25 @@ def test_intersection(self, closed, sort):
         result = index.intersection(other)
         tm.assert_index_equal(result, expected)
 
+    def test_intersection_empty_result(self, closed, sort):
+        index = monotonic_index(0, 11, closed=closed)
+
+        # GH 19101: empty result, same dtype
+        other = monotonic_index(300, 314, closed=closed)
+        expected = empty_index(dtype="int64", closed=closed)
+        result = index.intersection(other, sort=sort)
+        tm.assert_index_equal(result, expected)
+
+        # GH 19101: empty result, different numeric dtypes -> common dtype is float64
+        other = monotonic_index(300, 314, dtype="float64", closed=closed)
+        result = index.intersection(other, sort=sort)
+        expected = other[:0]
+        tm.assert_index_equal(result, expected)
+
+        other = monotonic_index(300, 314, dtype="uint64", closed=closed)
+        result = index.intersection(other, sort=sort)
+        tm.assert_index_equal(result, expected)
+
     def test_difference(self, closed, sort):
         index = IntervalIndex.from_arrays([1, 0, 3, 2], [1, 2, 3, 4], closed=closed)
         result = index.difference(index[:1], sort=sort)