Consider NaNs equal when comparing cubes

docs/src/whatsnew/latest.rst

@@ -91,7 +91,10 @@ This document explains the changes made to Iris for this release
 💣 Incompatible Changes
 =======================
 
-#. N/A
+#. `@bouweandela`_ and  `@trexfeathers`_ (reviewer) updated :class:`~iris.cube.Cube`
+   comparison so equality is now possible between cubes with data containing a
+   :obj:`numpy.nan`. e.g. ``Cube([np.nan, 1.0]) == Cube([np.nan, 1.0])`` will now
+   evaluate to :obj:`True`, while previously this would have been :obj:`False`. (:pull:`5713`)
 
 
 🚀 Performance Enhancements
@@ -113,6 +116,9 @@ This document explains the changes made to Iris for this release
 
 #. `@bouweandela`_ made comparing coordinates and arrays to themselves faster. (:pull:`5691`)
 
+#. `@bouweandela`_ and  `@trexfeathers`_ (reviewer) made comparing cubes to
+   themselves faster. (:pull:`5713`)
+
 
 🔥 Deprecations
 ===============

lib/iris/cube.py

@@ -3824,6 +3824,9 @@ def _deepcopy(self, memo, data=None):
 
     # START OPERATOR OVERLOADS
     def __eq__(self, other):
+        if other is self:
+            return True
+
         result = NotImplemented
 
         if isinstance(other, Cube):
@@ -3862,7 +3865,13 @@ def __eq__(self, other):
             if result:
                 # TODO: why do we use allclose() here, but strict equality in
                 #  _DimensionalMetadata (via util.array_equal())?
-                result = da.allclose(self.core_data(), other.core_data()).compute()
+                result = bool(
+                    np.allclose(
+                        self.core_data(),
+                        other.core_data(),
+                        equal_nan=True,
+                    )
+                )
         return result
 
     # Must supply __ne__, Python does not defer to __eq__ for negative equality

lib/iris/tests/unit/cube/test_Cube.py

@@ -2841,11 +2841,20 @@ def test_unit_multiply(self):
 class Test__eq__data(tests.IrisTest):
     """Partial cube equality testing, for data type only."""
 
+    def test_cube_identical_to_itself(self):
+        cube = Cube([1.0])
+        self.assertTrue(cube == cube)
+
     def test_data_float_eq(self):
         cube1 = Cube([1.0])
         cube2 = Cube([1.0])
         self.assertTrue(cube1 == cube2)
 
+    def test_data_float_nan_eq(self):
+        cube1 = Cube([np.nan, 1.0])
+        cube2 = Cube([np.nan, 1.0])
+        self.assertTrue(cube1 == cube2)
+
     def test_data_float_eqtol(self):
         val1 = np.array(1.0, dtype=np.float32)
         # NOTE: Since v2.3, Iris uses "allclose".  Prior to that we used