def continuous_frequency(self, data_frame):
        """
            This method returns continuous frequency

            :param data_frame: the data frame
            :type data_frame: pandas.DataFrame
            :return cont_freq: frequency
            :rtype cont_freq: float

        """
        tap_timestamps = data_frame.td[data_frame.action_type==1]
        cont_freq = 1.0/(np.array(tap_timestamps[1:-1])-np.array(tap_timestamps[0:-2]))
        duration = math.ceil(data_frame.td[-1])

        return cont_freq, duration
This method returns continuous frequency

            :param data_frame: the data frame
            :type data_frame: pandas.DataFrame
            :return cont_freq: frequency
            :rtype cont_freq: float