Nested flatMap in spark - scala

Question

in the below given code snipet i have declared and rdd by parallelizing a List(1,2,3,4) what i wanted do was to append List(1,2,3,4) to each element of the above rdd. i did so by using nested flatMap function scince it can return multiple values for each element of a RDD .The code is as follows
val rand6=sc.parallelize(List(1,2,3,4))
val bv=sc.broadcast(List(5,6,7,8))
rand6.flatMap(s=>{
val c=List(1,2,3,4)
val a=List(s,c)
val b=a.flatMap(r=>r)
b
})
But I am getting the following Error
command-1095314872161512:74: error: type mismatch;
found : Any
required: scala.collection.GenTraversableOnce[?]
val b=a.flatMap(r=>r)
^
is is the problem with the syntax or we are not supposed to use flatMaps in this fashion
it would be very helpful if someone can help me to understand this

Answer 1

Try to add type wherever possible in your scala code
Depending on your question description came up with below solution
import org.apache.spark.broadcast.Broadcast
import org.apache.spark.rdd.RDD
object RandomDF {
def main(args: Array[String]): Unit = {
val spark = Constant.getSparkSess
val sc = spark.sparkContext
val rand6 : RDD[Int] =sc.parallelize(List(1,2,3,4))
val bv: Broadcast[List[Int]] =sc.broadcast(List(5,6,7,8))
val output = rand6.map( (s : Int)=>{
val c : List[Int] =List(1,2,3,4)
val a = s :: c
// val b = a.flatMap(r=>r)
// b
a
}).collect().toList
println(output)
}
}