def gait(self, x):
        """ 
            Extract gait features from estimated heel strikes and accelerometer data.

            :param x: The time series to assess freeze of gait on. This could be x, y, z or mag_sum_acc.
            :type x: pandas.Series
            :return number_of_steps: Estimated number of steps based on heel strikes [number of steps].
            :rtype number_of_steps: int
            :return velocity: Velocity (if distance is provided) [meters/second].
            :rtype velocity: float
            :return avg_step_length: Average step length (if distance is provided) [meters].
            :rtype avg_step_length: float
            :return avg_stride_length: Average stride length (if distance is provided) [meters].
            :rtyoe avg_stride_length: float
            :return cadence: Number of steps divided by duration [steps/second].
            :rtype cadence: float
            :return array step_durations: Step duration [seconds].
            :rtype step_durations: np.ndarray
            :return float avg_step_duration: Average step duration [seconds].
            :rtype avg_step_duration: float
            :return float sd_step_durations: Standard deviation of step durations [seconds].
            :rtype sd_step_durations: np.ndarray
            :return list strides: Stride timings for each side [seconds].
            :rtype strides: numpy.ndarray
            :return float avg_number_of_strides: Estimated number of strides based on alternating heel strikes [number of strides].
            :rtype avg_number_of_strides: float
            :return list stride_durations: Estimated stride durations [seconds].
            :rtype stride_durations: numpy.ndarray
            :return float avg_stride_duration: Average stride duration [seconds].
            :rtype avg_stride_duration: float
            :return float sd_step_durations: Standard deviation of stride durations [seconds].
            :rtype sd_step_duration: float
            :return float step_regularity: Measure of step regularity along axis [percentage consistency of the step-to-step pattern].
            :rtype step_regularity: float
            :return float stride_regularity: Measure of stride regularity along axis [percentage consistency of the stride-to-stride pattern].
            :rtype stride_regularity: float
            :return float symmetry: Measure of gait symmetry along axis [difference between step and stride regularity].
            :rtype symmetry: float
        """
        
        data = x
        
        strikes, _ = self.heel_strikes(data)

        step_durations = []
        for i in range(1, np.size(strikes)):
            step_durations.append(strikes[i] - strikes[i-1])

        avg_step_duration = np.mean(step_durations)
        sd_step_durations = np.std(step_durations)

        number_of_steps = np.size(strikes)

        strides1 = strikes[0::2]
        strides2 = strikes[1::2]

        stride_durations1 = []
        for i in range(1, np.size(strides1)):
            stride_durations1.append(strides1[i] - strides1[i-1])

        stride_durations2 = []
        for i in range(1, np.size(strides2)):
            stride_durations2.append(strides2[i] - strides2[i-1])

        strides = [strides1, strides2]
        stride_durations = [stride_durations1, stride_durations2]

        avg_number_of_strides = np.mean([np.size(strides1), np.size(strides2)])
        avg_stride_duration = np.mean((np.mean(stride_durations1),
                                    np.mean(stride_durations2)))
        sd_stride_durations = np.mean((np.std(stride_durations1),
                                    np.std(stride_durations2)))

        step_period = np.int(np.round(1 / avg_step_duration))
        stride_period = np.int(np.round(1 / avg_stride_duration))

        step_regularity, stride_regularity, symmetry = self.gait_regularity_symmetry(data,
                                                                                     average_step_duration=avg_step_duration, 
                                                                                     average_stride_duration=avg_stride_duration)

        cadence = None
        if self.duration:
            cadence = number_of_steps / self.duration
        

        velocity = None
        avg_step_length = None
        avg_stride_length = None
        
        if self.distance:
            velocity = self.distance / self.duration
            avg_step_length = number_of_steps / self.distance
            avg_stride_length = avg_number_of_strides / self.distance

        return [number_of_steps, cadence,
               velocity,
               avg_step_length,
               avg_stride_length,
               step_durations,
               avg_step_duration,
               sd_step_durations,
               strides,
               stride_durations,
               avg_number_of_strides,
               avg_stride_duration,
               sd_stride_durations,
               step_regularity,
               stride_regularity, 
               symmetry]
Extract gait features from estimated heel strikes and accelerometer data.

            :param x: The time series to assess freeze of gait on. This could be x, y, z or mag_sum_acc.
            :type x: pandas.Series
            :return number_of_steps: Estimated number of steps based on heel strikes [number of steps].
            :rtype number_of_steps: int
            :return velocity: Velocity (if distance is provided) [meters/second].
            :rtype velocity: float
            :return avg_step_length: Average step length (if distance is provided) [meters].
            :rtype avg_step_length: float
            :return avg_stride_length: Average stride length (if distance is provided) [meters].
            :rtyoe avg_stride_length: float
            :return cadence: Number of steps divided by duration [steps/second].
            :rtype cadence: float
            :return array step_durations: Step duration [seconds].
            :rtype step_durations: np.ndarray
            :return float avg_step_duration: Average step duration [seconds].
            :rtype avg_step_duration: float
            :return float sd_step_durations: Standard deviation of step durations [seconds].
            :rtype sd_step_durations: np.ndarray
            :return list strides: Stride timings for each side [seconds].
            :rtype strides: numpy.ndarray
            :return float avg_number_of_strides: Estimated number of strides based on alternating heel strikes [number of strides].
            :rtype avg_number_of_strides: float
            :return list stride_durations: Estimated stride durations [seconds].
            :rtype stride_durations: numpy.ndarray
            :return float avg_stride_duration: Average stride duration [seconds].
            :rtype avg_stride_duration: float
            :return float sd_step_durations: Standard deviation of stride durations [seconds].
            :rtype sd_step_duration: float
            :return float step_regularity: Measure of step regularity along axis [percentage consistency of the step-to-step pattern].
            :rtype step_regularity: float
            :return float stride_regularity: Measure of stride regularity along axis [percentage consistency of the stride-to-stride pattern].
            :rtype stride_regularity: float
            :return float symmetry: Measure of gait symmetry along axis [difference between step and stride regularity].
            :rtype symmetry: float