Fix pruning for cubes that contain single CAT variables

- Add tests that reproduce index error for single CAT pruning
- Modify a conditional statement in how pruning is processed

src/cr/cube/crunch_cube.py

@@ -237,7 +237,7 @@ def _as_array(self, include_missing=False, get_non_selected=False,
 
         if prune and not self.has_mr:
             # Remove columns and rows where marginal value is 0 or np.nan
-            if len(self.dimensions) == 1:
+            if len(self.dimensions) == 1 or len(res.shape) == 1:
                 margin = self.margin(
                     include_transforms_for_dims=include_transforms_for_dims,
                     axis=1,

tests/integration/test_crunch_cube.py

@@ -2005,3 +2005,11 @@ def test_row_unweighted_margin_when_has_means(self):
         ])
         actual = cube.margin(axis=1, weighted=False, prune=True)
         np.testing.assert_array_equal(actual, expected)
+
+    def test_ca_with_single_cat_pruning(self):
+        cube = CrunchCube(FIXT_CA_SINGLE_CAT)
+        # The last 0 of the expectation is not visible in whaam because of
+        # pruning, which is not the responsibility of cr.cube.
+        expected = np.array([79, 80, 70])
+        actual = cube.as_array(weighted=False, prune=True)
+        np.testing.assert_almost_equal(actual, expected)