Observable Current and Previous Value

there you go

options.asObservable()
    .scan( [ [],[] ] ) { seed, newValue in
        return [ seed[1], newValue ]
    }
    // optional, working with tuple of array is better than array of array
    .map { array in (array[0], array[1])  } 
    //optional, in case you dont want empty array
    .skipWhile { $0.count == 0 && $1.count == 0 }

it will return Observable<([Options], [Options])> :)

Another way as an extension

extension ObservableType {

  func withPrevious() -> Observable<(E?, E)> {
    return scan([], accumulator: { (previous, current) in
        Array(previous + [current]).suffix(2)
      })
      .map({ (arr) -> (previous: E?, current: E) in
        (arr.count > 1 ? arr.first : nil, arr.last!)
      })
  }
}

Usage:

someValue
  .withPrevious()
  .subscribe(onNext: { (previous, current) in
    if let previous = previous { // previous is optional
      print("previous: \(previous)")
    }
    print("current: \(current)")
  })
  .disposed(by: disposeBag)

Here is a handy generic extension, that should cover these "I want the previous and the current value" use cases:

extension ObservableType {

    func withPrevious(startWith first: E) -> Observable<(E, E)> {
        return scan((first, first)) { ($0.1, $1) }.skip(1)
    }
}