BUG: IntervalIndex.unique() only contains the first interval if all interval borders are negative

pandas/core/arrays/interval.py

@@ -1971,10 +1971,10 @@ def _from_combined(self, combined: np.ndarray) -> IntervalArray:
         """
         Create a new IntervalArray with our dtype from a 1D complex128 ndarray.
         """
-        nc = combined.view("i8").reshape(-1, 2)
 
         dtype = self._left.dtype
         if needs_i8_conversion(dtype):
+            nc = combined.view("i8").reshape(-1, 2)
             assert isinstance(self._left, (DatetimeArray, TimedeltaArray))
             new_left: DatetimeArray | TimedeltaArray | np.ndarray = type(
                 self._left
@@ -1985,6 +1985,9 @@ def _from_combined(self, combined: np.ndarray) -> IntervalArray:
             )._from_sequence(nc[:, 1], dtype=dtype)
         else:
             assert isinstance(dtype, np.dtype)
+            nc = np.hstack(
+                [np.real(combined).astype(dtype), np.imag(combined).astype(dtype)]
+            ).reshape(-1, 2)
             new_left = nc[:, 0].view(dtype)
             new_right = nc[:, 1].view(dtype)
         return self._shallow_copy(left=new_left, right=new_right)

pandas/tests/arrays/interval/test_interval.py

@@ -117,19 +117,24 @@ def test_unique_with_negatives(self):
             [(3, 4), (3, 4), (2, 3), (2, 3), (1, 2), (1, 2)]
         )
         result = idx_pos.unique()
-        assert result.shape == (3,), f"Expected shape (3,), got {result.shape}"
+        expected = IntervalIndex.from_tuples([(3, 4), (2, 3), (1, 2)])
+        tm.assert_index_equal(result, expected)
 
         idx_neg = IntervalIndex.from_tuples(
             [(-4, -3), (-4, -3), (-3, -2), (-3, -2), (-2, -1), (-2, -1)]
         )
         result = idx_neg.unique()
-        assert result.shape == (3,), f"Expected shape (3,), got {result.shape}"
+        expected = IntervalIndex.from_tuples([(-4, -3), (-3, -2), (-2, -1)])
+        tm.assert_index_equal(result, expected)
 
         idx_mix = IntervalIndex.from_tuples(
             [(1, 2), (0, 1), (-1, 0), (-2, -1), (-3, -2), (-3, -2)]
         )
         result = idx_mix.unique()
-        assert result.shape == (5,), f"Expected shape (5,), got {result.shape}"
+        expected = IntervalIndex.from_tuples(
+            [(1, 2), (0, 1), (-1, 0), (-2, -1), (-3, -2)]
+        )
+        tm.assert_index_equal(result, expected)
 
 
 class TestSetitem: