def reduce_all_results(contacts):
    """Combine multiple :class:`.ContactFrequency` objects into one

    Parameters
    ----------
    contacts : iterable of :class:`.ContactFrequency`
        the individual (partial) contact frequencies

    Returns
    -------
    :class:`.ContactFrequency` :
        total of all input contact frequencies (summing them)
    """
    accumulator = contacts[0]
    for contact in contacts[1:]:
        accumulator.add_contact_frequency(contact)
    return accumulator
