Ratio of values that are more than r*std(x) (so r sigma) away from the mean of x.

    :param x: the time series to calculate the feature of
    :type x: iterable
    :return: the value of this feature
    :return type: float

def ratio_beyond_r_sigma(x, r):
    """
    Ratio of values that are more than r*std(x) (so r sigma) away from the mean of x.

    :param x: the time series to calculate the feature of
    :type x: iterable
    :return: the value of this feature
    :return type: float
    """
    if not isinstance(x, (np.ndarray, pd.Series)):
        x = np.asarray(x)
    return np.sum(np.abs(x - np.mean(x)) > r * np.std(x))/x.size