def ARGMAX(agg_column, out_column):
    """
  Builtin arg maximum aggregator for groupby

  Example: Get the movie with maximum rating per user.

  >>> sf.groupby("user",
  ...            {'best_movie':gl.aggregate.ARGMAX('rating','movie')})
  """
    return '__builtin__argmax__', [agg_column, out_column]
