merged with upstream master

Author: jeet63

pandas/core/algorithms.py

@@ -988,9 +988,12 @@ def _get_data_algo(values, func_map):
     elif is_unsigned_integer_dtype(values):
         f = func_map['uint64']
         values = _ensure_uint64(values)
-    elif is_categorical(values) and values._ordered:
-        f = func_map['float64']
+    elif is_categorical_dtype(values):
         values = values._values_for_rank()
+        if is_float_dtype(values):
+            f = func_map['float64']
+        else:
+            f = func_map['object']
     else:
         values = _ensure_object(values)
 

pandas/core/categorical.py

@@ -1416,10 +1416,14 @@ def _values_for_rank(self):
         numpy array
 
         """
-        values = self._codes.astype('float64')
-        if self._ordered:
-            na_mask = (values == -1)
-            values[na_mask] = np.nan
+        if self.ordered:
+            values = self.codes
+            mask = values == -1
+            if mask.any():
+                values = values.astype('float64')
+                values[mask] = np.nan
+        else:
+            values = np.array(self)
         return values
 
     def order(self, inplace=False, ascending=True, na_position='last'):