def preprocess_identity(*data, categorical_variables=None):
    """    
    An identify function for preprocessing.

    Returns inputs without modifying them.

    :param data: array(s).
    :param categorical_variables: A list of strings representing the variables that are categorical.
    :return: array(s).
    """
    if len(data) == 1:
        output = data[0]
    elif len(data) == 2:
        output = data[0], data[1]
    else:
        raise ValueError
    return output
