Update in cast handling

Author: radekbenesinno

pandas/core/groupby/base.py

@@ -89,7 +89,8 @@ def _gotitem(self, key, ndim, subset=None):
 cython_transforms = frozenset(['cumprod', 'cumsum', 'shift',
                                'cummin', 'cummax'])
 
-cython_cast_blacklist = frozenset(['rank', 'count', 'size'])
+cython_cast_blacklist = frozenset(['rank', 'count', 'size', 'idxmin',
+                                   'idxmax'])
 
 
 def whitelist_method_generator(base, klass, whitelist):

pandas/core/groupby/generic.py

@@ -255,8 +255,10 @@ def _aggregate_item_by_item(self, func, *args, **kwargs):
                 colg = SeriesGroupBy(data, selection=item,
                                      grouper=self.grouper)
 
+                cast = self._transform_should_cast(func)
+
                 result[item] = colg.aggregate(func, *args, **kwargs)
-                if func != "idxmin" and func != "idxmax":
+                if cast:
                     result[item] = self._try_cast(result[item], data)
 
             except ValueError: