def subset_data(data, col):
    """
    Creates list of categories for column used to populate
    dropdown menus

    :param data: pd.DataFrame
        generated from app_wrangling.call_boardgame_data()
    :param col: string, column generate list for

    :return list(exp_series.unique()): list of strings
    """

    boardgame_data = data.copy(deep=True)
    exp_series = boardgame_data[col].explode()
    return list(exp_series.unique())