def pb_opponent_id(df, order=0):
    """
    Get the opponent id from a pick / ban Frame.

    Parameters
    ----------
    df : DataFrame
        formatted like a pick / ban frame
    order : int
        pick / ban order (1 .. 19)

    Returns
    -------
    opponent_id : int
    """
    x = df['team_id_f'].unique()
    other_team = {x[0]: x[1], x[1]: x[0]}
    return df.team_id_f.map(other_team).iloc[order]