GH#15420 added support for na_option when ranking categorical

Author: jeet63

doc/source/whatsnew/v0.20.0.txt

@@ -628,3 +628,4 @@ Bug Fixes
 - Bug in ``Series.replace`` and ``DataFrame.replace`` which failed on empty replacement dicts (:issue:`15289`)
 - Bug in ``pd.melt()`` where passing a tuple value for ``value_vars`` caused a ``TypeError`` (:issue:`15348`)
 - Bug in ``.eval()`` which caused multiline evals to fail with local variables not on the first line (:issue:`15342`)
+- Bug in ``.rank()`` rank incorrectly orders ordered categories

pandas/tests/series/test_analytics.py

@@ -1059,13 +1059,14 @@ def test_rank(self):
 
     def test_rank_categorical(self):
         # GH issue #15420 rank incorrectly orders ordered categories
-
+        
         # Test ascending/descending ranking for ordered categoricals
         exp = pd.Series([1., 2., 3., 4., 5., 6.])
         exp_desc = pd.Series([6., 5., 4., 3., 2., 1.])
-        ordered = pd.Series(
-            ['first', 'second', 'third', 'fourth', 'fifth', 'sixth'],
-        ).astype('category').cat.set_categories(
+        ser = pd.Series(
+            ['first', 'second', 'third', 'fourth', 'fifth', 'sixth']
+        )
+        ordered = ser.astype('category', ).cat.set_categories(
             ['first', 'second', 'third', 'fourth', 'fifth', 'sixth'],
             ordered=True
         )
@@ -1088,6 +1089,15 @@ def test_rank_categorical(self):
             ['first', 'second', 'third', 'fourth', 'fifth', 'sixth', np.NaN],
         ).astype('category').cat.set_categories(
             ['first', 'second', 'third', 'fourth', 'fifth', 'sixth'],
+
+        # Test na_option for rank data
+        na_ser = pd.Series(
+            ['first', 'second', 'third', 'fourth', 'fifth', 'sixth', np.NaN]
+        ).astype('category', ).cat.set_categories(
+            [
+                'first', 'second', 'third', 'fourth',
+                'fifth', 'sixth', 'seventh'
+            ],
             ordered=True
         )
 

pandas/tests/test_categorical.py

@@ -4549,14 +4549,6 @@ def test_concat_categorical(self):
                             'h': [None] * 6 + cat_values})
         tm.assert_frame_equal(res, exp)
 
-    def test_rank_categorical(self):
-        exp = pd.Series([1., 2., 3., 4., 5., 6.], name='A')
-        dframe = pd.DataFrame(['first', 'second', 'third', 'fourth', 'fifth', 'sixth'], columns=['A'])
-        dframe['A'] = dframe['A'].astype('category', ).cat.set_categories(
-                ['first', 'second', 'third', 'fourth', 'fifth', 'sixth'], ordered=True)
-        res = dframe['A'].rank()
-        tm.assert_series_equal(res, exp)
-
 class TestCategoricalSubclassing(tm.TestCase):
 
     def test_constructor(self):