def AVG(src_column):
    """
    Builtin average aggregator for groupby. Synonym for tc.aggregate.MEAN. 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_avg':tc.aggregate.AVG('rating')})
    """
    return '__builtin__avg__', [src_column]
