def apply_title_filter(df, f):
    """Applies f on the title to get filtered results

    Parameters
    ----------
    df: DataFrame
        source data
    f: function
        a function that accepts a dataframe and a field name. and returns a boolean flag.

    Returns
    -------
    DataFrame
        a dataframe filtered based on f

    """
    title_flag = f(df, "title")
    return df[title_flag.fillna(False)]