cubepart: add CubePartition.cube_index

src/cr/cube/cubepart.py

@@ -56,6 +56,14 @@ def factory(
             )
         return _Slice(cube, slice_idx, transforms, population, mask_size)
 
+    @lazyproperty
+    def cube_index(self):
+        """Offset of this partition's cube in its CubeSet.
+
+        Used to differentiate certain partitions like a filtered rows-summary strand.
+        """
+        return self._cube.cube_index
+
     @lazyproperty
     def cube_is_mr_by_itself(self):
         return False

tests/integration/test_cubepart.py

@@ -1023,6 +1023,7 @@ def it_provides_values_for_univariate_cat(self):
         assert strand.base_counts == (10, 5)
         assert strand.bases == (15, 15)
         assert strand.counts == (10, 5)
+        assert strand.cube_index == 0
         assert strand.cube_is_mr_by_itself is False
         assert strand.dimension_types == (DT.CAT,)
         assert strand.has_means is False

tests/unit/test_cubepart.py

@@ -52,6 +52,14 @@ def and_it_constructs_a_nub_for_a_0D_cube(self, request, cube_):
         _Nub_.assert_called_once_with(cube_)
         assert nub is _Nub_.return_value
 
+    def it_knows_the_index_of_its_cube_in_the_cube_set(self, cube_):
+        cube_.cube_index = 42
+        cube_partition = CubePartition(cube_)
+
+        cube_index = cube_partition.cube_index
+
+        assert cube_index == 42
+
     def it_knows_if_cube_is_mr_by_itself(self):
         # --- default of False is overridden by subclasses when appropriate ---
         assert CubePartition(None).cube_is_mr_by_itself is False