Randomly choose a given number of moves from the last n games.

        Args:
          n:  number of games at the end of this GameQueue to source.
          moves:  number of moves to be sampled from `n` games.
          shuffle:  if True, shuffle the selected moves.
          column_family:  name of the column family containing move examples.
          column:  name of the column containing move examples.

        Returns:
          a dataset containing the selected moves.

def moves_from_last_n_games(self, n, moves, shuffle,
                                column_family, column):
        """Randomly choose a given number of moves from the last n games.

        Args:
          n:  number of games at the end of this GameQueue to source.
          moves:  number of moves to be sampled from `n` games.
          shuffle:  if True, shuffle the selected moves.
          column_family:  name of the column family containing move examples.
          column:  name of the column containing move examples.

        Returns:
          a dataset containing the selected moves.
        """
        self.wait_for_fresh_games()
        latest_game = self.latest_game_number
        utils.dbg('Latest game in %s: %s' % (self.btspec.table, latest_game))
        if latest_game == 0:
            raise ValueError('Cannot find a latest game in the table')

        start = int(max(0, latest_game - n))
        ds = self.moves_from_games(start, latest_game, moves, shuffle,
                                   column_family, column)
        return ds