def select_column_values(df, col_name="totale_casi", groupby=["data"], group_by_criterion="sum"):
    """

    :param df: pandas dataFrame
    :param col_name: column of interest
    :param groupby: column to group by (optional) data.
    :param group_by_criterion: how to merge the values of grouped elements in col_name.
    Only sum supported.
    :return: a list of of values
    """
    if groupby is not None:
        if group_by_criterion == "sum":
            return df.groupby(by=groupby)[col_name].sum().reset_index()[col_name].values
        else:
            return RuntimeWarning
    else:
        return list(df[col_name])