Allow for dict-like argument to Categorical.rename_categories

Author: alanbato

doc/source/whatsnew/v0.21.0.txt

@@ -114,7 +114,7 @@ Other Enhancements
 - :func:`pd.read_sas()` now recognizes much more of the most frequently used date (datetime) formats in SAS7BDAT files (:issue:`15871`).
 - :func:`DataFrame.items` and :func:`Series.items` is now present in both Python 2 and 3 and is lazy in all cases (:issue:`13918`, :issue:`17213`)
 - :func:`Styler.where` has been implemented. It is as a convenience for :func:`Styler.applymap` and enables simple DataFrame styling on the Jupyter notebook (:issue:`17474`).
-
+- :func:`Categorical.rename_categories` now accepts a dict-like argument as `new_categories`, and only updates the categories found in that dict. (:issue:`17336`)
 
 
 .. _whatsnew_0210.api_breaking:

pandas/core/categorical.py

@@ -824,7 +824,11 @@ def rename_categories(self, new_categories, inplace=False):
         """
         inplace = validate_bool_kwarg(inplace, 'inplace')
         cat = self if inplace else self.copy()
-        cat.categories = new_categories
+        if isinstance(new_categories, dict):
+            cat.categories = [new_categories.get(item, item)
+                              for item in cat.categories]
+        else:
+            cat.categories = new_categories
         if not inplace:
             return cat
 

pandas/tests/test_categorical.py

@@ -983,6 +983,18 @@ def test_rename_categories(self):
         with pytest.raises(ValueError):
             cat.rename_categories([1, 2])
 
+    def test_rename_categories_dict(self):
+        # GH 17336
+        cat = pd.Categorical(['a', 'b', 'c', 'd'])
+        res = cat.rename_categories({'a': 4, 'b': 3, 'c': 2, 'd': 1})
+        expected = Index([4, 3, 2, 1])
+        tm.assert_index_equal(res.categories, expected)
+        # Test for inplace
+        res = cat.rename_categories({'a': 4, 'b': 3, 'c': 2, 'd': 1},
+                                    inplace=True)
+        assert res is None
+        tm.assert_index_equal(cat.categories, expected)
+
     @pytest.mark.parametrize('codes, old, new, expected', [
         ([0, 1], ['a', 'b'], ['a', 'b'], [0, 1]),
         ([0, 1], ['b', 'a'], ['b', 'a'], [0, 1]),