Use functional style to fill a set instead of a loop

In scala you should feel encouraged to use a more functional style of programming instead of the imperative paradigm that you might be used to.

So instead of initializing a Set and then filling it, the functional way of doing this is to create values in a functional flow and then assign them once. This way you can use an immutable Set and a val instead of a var and a mutable type. You want to avoid vars and mutable types because they carry state and might not be filled properly.

So instead of this imperative approach where you end up with a var that could be reassigned or changed:

#create a list of tuples that we are going to work with
val objectList = Array(("0", "a"), ("1", "b"))

#initiate an empty mutable set
var signalList: Set[String] = Set[String]()

for (object <- objectList) {
    signalList += object._1
    signalList += object._2
}

… you could write this more functional version with the same functionality:

#create a list of tuples that we are going to work with
val objectList = Array(("0", "a"), ("1", "b"))

val signalList: Set[String] = objectList.flatMap(obj => Array(obj._1, obj._2))
                                        .toSet

From the scala docs:

FlatMap

def flatMap[BS, B](f: (T) => BS)(implicit asIterable: (BS) => collection.Iterable[B], m: ClassTag[B]): Array[B]

Implicit: This member is added by an implicit conversion from Array[T] toArrayOps[T] performed by method genericArrayOps in scala.Predef.

Definition Classes: ArrayOps

Use functional style to fill a set instead of a loop (Aug 12, 2020)

From the scala docs: