def union(other)
      if self.serializer != other.serializer
        other = other.reserialize(serializer)
      end

      new_jrdd = jrdd.union(other.jrdd)
      RDD.new(new_jrdd, context, serializer, deserializer)
    end
def union(other)
      if self.serializer != other.serializer
        other = other.reserialize(serializer)
      end

      new_jrdd = jrdd.union(other.jrdd)
      RDD.new(new_jrdd, context, serializer, deserializer)
    end
Return the union of this RDD and another one. Any identical elements will appear multiple
 times (use .distinct to eliminate them).

 == Example:
   rdd = $sc.parallelize([1, 2, 3])
   rdd.union(rdd).collect
   # => [1, 2, 3, 1, 2, 3]