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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 top(self, num, key=None):
 """ Get the top N elements from an RDD. .. note:: This method should only be used if the resulting array is expected to be small, as all the data is loaded into the driver's memory. .. note:: It returns the list sorted in descending order. [12] [6, 5] [4, 3, 2] """

        def topIterator(iterator):
            yield heapq.nlargest(num, iterator, key=key)

        def merge(a, b):
            return heapq.nlargest(num, a + b, key=key)

        return self.mapPartitions(topIterator).reduce(merge)