docs: 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