code: def countApproxDistinct(self, relativeSD=0.05):
          
          if relativeSD < 0.000017:
              raise ValueError("relativeSD should be greater than 0.000017")
          # the hash space in Java is 2^32
          hashRDD = self.map(lambda x: portable_hash(x) & 0xFFFFFFFF)
          return hashRDD._to_java_object_rdd().countApproxDistinct(relativeSD)
docs: .. note:: Experimental
  
          Return approximate number of distinct elements in the RDD.
  
          The algorithm used is based on streamlib's implementation of
          `"HyperLogLog in Practice: Algorithmic Engineering of a State
          of The Art Cardinality Estimation Algorithm", available here
          <https://doi.org/10.1145/2452376.2452456>`_.
  
          :param relativeSD: Relative accuracy. Smaller values create
                             counters that require more space.
                             It must be greater than 0.000017.
  
          >>> n = sc.parallelize(range(1000)).map(str).countApproxDistinct()
          >>> 900 < n < 1100
          True
          >>> n = sc.parallelize([i % 20 for i in range(1000)]).countApproxDistinct()
          >>> 16 < n < 24
          True