REGR: Fix IntervalArray.nunique with infinity (#63267)

Author: rhshadrach

pandas/core/arrays/interval.py

@@ -2128,9 +2128,8 @@ def _combined(self) -> IntervalSide:
             )
             comb = comb.view("complex128")[:, 0]
         else:
-            comb = (np.array(left.ravel(), dtype="complex128")) + (
-                1j * np.array(right.ravel(), dtype="complex128")
-            )
+            comb = np.asarray(left.ravel(), dtype="complex128")
+            comb.imag = right.ravel()
         return comb
 
     def _from_combined(self, combined: np.ndarray) -> IntervalArray:

pandas/tests/arrays/interval/test_interval.py

@@ -136,6 +136,20 @@ def test_unique_with_negatives(self):
         )
         tm.assert_index_equal(result, expected)
 
+    @pytest.mark.parametrize(
+        "data",
+        [
+            [Interval(-np.inf, 0), Interval(-np.inf, 1)],
+            [Interval(0, np.inf), Interval(1, np.inf)],
+        ],
+    )
+    def test_unique_with_infinty(self, data):
+        # https://github.com/pandas-dev/pandas/issues/63218
+        s = pd.Series(data)
+        tm.assert_interval_array_equal(s.unique(), s.array)
+        assert s.nunique() == 2
+        tm.assert_series_equal(s.drop_duplicates(), s)
+
 
 class TestSetitem:
     def test_set_na(self, left_right_dtypes):