Transaction.swift

class TransactionStore {
  var shared: TransactionStore = TransactionStore()
  
  var transactions: Variable<[Transaction]>
  
}

// ViewModel
class Presenter {
  
  var monthsOfDataBeforeToday: Variable<Int> = ...
  
  var transactions: Observable<[Transaction]> {
    return Observable.combineLatest(TransactionStore.shared.transactions.asObservable(), monthsOfDataBeforeToday.asObservable()){ (transactions, months)
        return transactions.filter(months) // write a real filter function with `months` variable
    }
  }
}

class ViewController: UIViewController {

  var presenter = Presenter()
  
  func viewDidLoad() {
    ...
    presenter.transactions.subscribe(onNext: { transactions in
       // reloadview
    })
  }
  
  func segmentedControlSelected(index: Int) {
    presenter.monthsOfDataBeforeToday.value = [4, 6, 12][index]
    // now view will auto reload cause setting this will trigger presenter.transactions onnext
  }
    
  
}