Return a new DStream in which each RDD contains the count of distinct elements in
RDDs in a sliding window over this DStream.
width of the window; must be a multiple of this DStream’s
sliding interval of the window (i.e., the interval after which
the new DStream will generate RDDs); must be a multiple of this
DStream’s batching interval
number of partitions of each RDD in the new DStream.