def process_cabin(df):
    """
    Converts the Cabin column into pre-defined bins.

    :param df: Dataframe
    :return: Dataframe with Cabin column having pre-defined bins
    """
    df["Cabin_type"] = df["Cabin"].str[0]
    df["Cabin_type"] = df["Cabin_type"].fillna("Unknown")
    df = df.drop('Cabin', axis=1)
    return df