How do I append values fo an observed array in RxSwift

Trying to grasp RxSwift and get stuck on a few things.

var observedData = BehaviorSubject.from([2, 3, 4, 5, 6])
    .map({$0*3}).subscribe(onNext: {
        print("HELLO", $0)
    })

How do I append an extra value to the array, so that the subscription is triggered again?

I tried observedData.onNext and observedData.accept but they don't work.

I also would like to know the difference between

var observedData = BehaviorSubject.from([2, 3, 4, 5, 6])

and

var observedData2 = BehaviorSubject<[Int]>(value: [2, 3, 4, 5, 6])

I first assumed it was different ways of writing the same thing, but I can't use .map on observedData2

Along with the answer @EtienneJézéquel gave...

The public static func ObservableType.from(_:) function returns an Observable whereas the BehaviorSubject.init(value:) creates a BehaviorSubject which must then be converted to an Observable before you can map(_:) it.

Also, it might help to understand better when you realize you don't append to the array that is contained by the BehaviorSubject, instead you emit a new array using it. That's why Etienne's code first copies the current array out of the subject using value() throws and appends to the copy and then pushes the new array into the subject using onNext(_:).

Lastly, don't make subjects vars they should always be lets because you don't want to reseat them after setting up chains to them.

something like that should work :

let subject = BehaviorSubject<[Int]>(value: [2, 3, 4, 5, 6])
subject.asObservable().map({$0.map({$0*3})}).subscribe(onNext: { print("HELLO", $0) }).disposed(by: disposeBag)
if var value = try? subject.value() {
    value.append(1)
    subject.on(.next(value))
}