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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def map_series(self, fn, dt_index = None):
 """ 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. """

        if dt_index == None:
          dt_index = self.index()
        return TimeSeriesRDD(dt_index, self.map(fn))