tokenize input and subscribe. Instant profit when combined with JSON object async response stuff.

gistfile1.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Reactive;
using System.Reactive.Linq;
using System.Reactive.Concurrency;
using System.Reactive.Subjects;

namespace ReactiveTest
{
    static class ReactiveExtension
    {
        public static IDisposable SubscribeOnKey(this IObservable<KeyValuePair<int, string>> source, int key, Action<string> subscribe)
        {
            return source.Where(x => x.Key == key).Select(x => x.Value).Subscribe(subscribe);
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            var src = GetInput().ToObservable(Scheduler.NewThread);

            var res = from s in src group s by s.Length;
            Subject<KeyValuePair<int, string>> streamsByKey = new Subject<KeyValuePair<int,string>>();
            res.Subscribe(x => {
                x.Subscribe(x_ => { streamsByKey.OnNext(new KeyValuePair<int, string>(x.Key, x_)); });
            });

            streamsByKey.SubscribeOnKey(5, x => Console.WriteLine("Profit with " + x));
            streamsByKey.SubscribeOnKey(7, x => Console.WriteLine("Also we has " + x));
            streamsByKey.SubscribeOnKey(9, x => Console.WriteLine("Als... shit: " + x));
        }

        static IEnumerable<string> GetInput()
        {
            while(true) yield return Console.ReadLine();
        }
    }
}