def MEAN(src_column):
  """
  Builtin average aggregator for groupby. Synonym for tc.aggregate.AVG. If
  src_column is of array type, and if array's do not match in length a NoneType is
  returned in the destination column.


  Example: Get the average rating of each user.

  >>> sf.groupby("user",
  ...            {'rating_mean':tc.aggregate.MEAN('rating')})

  """
  return ("__builtin__avg__", [src_column])