Reactive Extensions And/Then/When FizzBuzz

RxAndThenWhenFizzBuzz.cs

using System;
using System.Linq;
using System.Reactive.Linq;

namespace RxAndThenWhenFizzBuzz {
    class Program {
        static void Main(string[] args) {
            var numberObserver = Observable.Range(1, 30);
            var fizzObserver = numberObserver.Select(i => i % 3 == 0 ? "Fizz" : "");
            var buzzObserver = numberObserver.Select(i => i % 5 == 0 ? "Buzz" : "");

            var plan = numberObserver
                .And(fizzObserver)
                .And(buzzObserver)
                .Then((i, f, b) => f + b == "" ? i.ToString() : f + b);
                
            Observable.When(plan).Subscribe(Console.WriteLine);

            Console.ReadKey();
        }
    }
}

result

1
2
Fizz
4
Buzz
Fizz
7
8
Fizz
Buzz
11
Fizz
13
14
FizzBuzz
16
17
Fizz
19
Buzz
Fizz
22
23
Fizz
Buzz
26
Fizz
28
29
FizzBuzz