tests for categorical index monotonicity

pandas/core/indexes/category.py

@@ -316,10 +316,23 @@ def _engine(self):
         # we are going to look things up with the codes themselves
         return self._engine_type(lambda: self.codes.astype('i8'), len(self))
 
+    # introspection
     @cache_readonly
     def is_unique(self):
         return not self.duplicated().any()
 
+    @property
+    def is_monotonic(self):
+        return self.is_monotonic_increasing
+
+    @property
+    def is_monotonic_increasing(self):
+        return Index(self.codes).is_monotonic_increasing
+
+    @property
+    def is_monotonic_decreasing(self):
+        return Index(self.codes).is_monotonic_decreasing
+
     @Appender(base._shared_docs['unique'] % _index_doc_kwargs)
     def unique(self):
         result = base.IndexOpsMixin.unique(self)

pandas/tests/indexes/test_category.py

@@ -427,6 +427,38 @@ def test_reindex_empty_index(self):
         tm.assert_numpy_array_equal(indexer,
                                     np.array([-1, -1], dtype=np.intp))
 
+    def test_is_monotonic(self):
+        c = CategoricalIndex([1, 2, 3])
+        assert c.is_monotonic_increasing
+        assert not c.is_monotonic_decreasing
+
+        c = CategoricalIndex([1, 2, 3], ordered=True)
+        assert c.is_monotonic_increasing
+        assert not c.is_monotonic_decreasing
+
+        c = CategoricalIndex([1, 2, 3], categories=[3, 2, 1])
+        assert not c.is_monotonic_increasing
+        assert c.is_monotonic_decreasing
+
+        c = CategoricalIndex([1, 3, 2], categories=[3, 2, 1])
+        assert not c.is_monotonic_increasing
+        assert not c.is_monotonic_decreasing
+
+        c = CategoricalIndex([1, 2, 3], categories=[3, 2, 1], ordered=True)
+        assert not c.is_monotonic_increasing
+        assert c.is_monotonic_decreasing
+
+        # non lexsorted categories
+        categories = [9, 0, 1, 2, 3]
+
+        c = CategoricalIndex([9, 0], categories=categories)
+        assert c.is_monotonic_increasing
+        assert not c.is_monotonic_decreasing
+
+        c = CategoricalIndex([0, 1], categories=categories)
+        assert c.is_monotonic_increasing
+        assert not c.is_monotonic_decreasing
+
     def test_duplicates(self):
 
         idx = CategoricalIndex([0, 0, 0], name='foo')

pandas/tests/reshape/test_concat.py

@@ -1934,7 +1934,6 @@ def test_concat_categoricalindex(self):
         c = pd.Series(3, index=pd.CategoricalIndex([1, 2],
                                                    categories=categories))
 
-        import pdb; pdb.set_trace()
         result = pd.concat([a, b, c], axis=1)
 
         exp_idx = pd.CategoricalIndex([0, 1, 2, 9])