TST: test for categorical index monotonicity (#17152)

* correctly determine bottleneck version

* tests for categorical index monotonicity

* fix Index.is_monotonic to point to Index.is_monotonic_increasing directly

Author: jreback

Diff for: pandas/core/indexes/base.py

@@ -1195,7 +1195,7 @@ def _mpl_repr(self):
     @property
     def is_monotonic(self):
         """ alias for is_monotonic_increasing (deprecated) """
-        return self._engine.is_monotonic_increasing
+        return self.is_monotonic_increasing
 
     @property
     def is_monotonic_increasing(self):

Diff for: pandas/core/indexes/category.py

@@ -316,10 +316,19 @@ 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_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)

Diff for: pandas/core/nanops.py

@@ -28,7 +28,8 @@
 try:
     import bottleneck as bn
     ver = bn.__version__
-    _BOTTLENCK_INSTALLED = ver >= LooseVersion(_MIN_BOTTLENECK_VERSION)
+    _BOTTLENECK_INSTALLED = (LooseVersion(ver) >=
+                             LooseVersion(_MIN_BOTTLENECK_VERSION))
 
     if not _BOTTLENECK_INSTALLED:
         warnings.warn(

Diff for: 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')