code: def _mixup( self, ps ):
          
          for i in range(len(ps) - 1, 0, -1):
              j = int(numpy.random.random() * i)
              temp = ps[i]
              ps[i] = ps[j]
              ps[j] = temp
          return ps
docs: Private method to mix up a list of values in-place using a Fisher-Yates
          shuffle (see https://en.wikipedia.org/wiki/Fisher-Yates_shuffle).
  
          :param ps: the array
          :returns: the array, shuffled in-place