code: def map_series(self, fn, dt_index = None):
          
          if dt_index == None:
            dt_index = self.index()
          return TimeSeriesRDD(dt_index, self.map(fn))
docs: Returns a TimeSeriesRDD, with a transformation applied to all the series in this RDD.
  
          Either the series produced by the given function should conform to this TimeSeriesRDD's
          index, or a new DateTimeIndex should be given that they conform to.
          
          Parameters
          ----------
          fn : function
              A function that maps arrays of floats to arrays of floats.
          dt_index : DateTimeIndex
              A DateTimeIndex for the produced TimeseriesRDD.