def COUNT_DISTINCT(src_column):
    """
  Builtin unique counter for groupby. Counts the number of unique values

  Example: Get the number of unique ratings produced by each user.

  >>> sf.groupby("user",
  ...    {'rating_distinct_count':gl.aggregate.COUNT_DISTINCT('rating')})

  """
    return '__builtin__count__distinct__', [src_column]
