def flip(k:Any,v:Any):(Any,Any) = (v,k)

val word_count = words map {sentWords => sentWords map (w => (w.toLowerCase,1))} flatMap {ws => ws} reduceByKey (_ + _) map { case (k,v) => (v,k) } //works ok

val word_count = words map {sentWords => sentWords map (w => (w.toLowerCase,1))} flatMap {ws => ws} reduceByKey (_ + _) map flip //doesnt work