code: def normalize(data):
      
      data = data.astype(float)
      data -= data.mean()
      
      return data / data.std()
docs: Function to normalize data to have mean 0 and unity standard deviation
      (also called z-transform)
      
      
      Parameters
      ----------
      data : numpy.ndarray
      
      
      Returns
      -------
      numpy.ndarray
          z-transform of input array