performance_rxswift.swift

Observable.from(fahrenheit)
    .map({ (degreesFahrenheit) -> Double in
        return (degreesFahrenheit - 32.0) / 1.8
    })
    .filter({ (degreesCelsius) -> Bool in
        return degreesCelsius <= 20.0
    })
    .reduce(0.0, accumulator: ({ (result, degreesCelsius) -> Double in
        return result + degreesCelsius
    }))
    .subscribe(onNext: { sum in
        print(sum)
    })
    .disposed(by: disposeBag)