fix the function signature of map to be consistent across different c…

…lasses

pandas/core/indexes/datetimelike.py

@@ -220,9 +220,9 @@ def __contains__(self, key):
 
     # Try to run function on index first, and then on elements of index
     # Especially important for group-by functionality
-    def map(self, f):
+    def map(self, mapper, na_action=None):
         try:
-            result = f(self)
+            result = mapper(self)
 
             # Try to use this result if we can
             if isinstance(result, np.ndarray):
@@ -232,7 +232,7 @@ def map(self, f):
                 raise TypeError('The map function must return an Index object')
             return result
         except Exception:
-            return self.astype(object).map(f)
+            return self.astype(object).map(mapper)
 
     def sort_values(self, return_indexer=False, ascending=True):
         """