Which function in spark is used to combine two RDDs by keys

Question

Let us say I have the following two RDDs, with the following key-pair values.

rdd1 = [ (key1, [value1, value2]), (key2         


        

Answer 1

I would union the two RDDs and to a reduceByKey to merge the values.

(rdd1 union rdd2).reduceByKey(_ ++ _)

Answer 2

Just use join and then map the resulting rdd.

rdd1.join(rdd2).map(case (k, (ls, rs)) => (k, ls ++ rs))