Example of Scatter Gather in Akka.NET

akkascattergather.cs

using System;
using Akka.Actor;
using Akka;
using Akka.Remote;
using Akka.Routing;
using System.Linq;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;

namespace Actors
{

	public class Hotel
	{

		public Hotel (string country, string city, string name)
		{
			Country = country;
			City = city;
			Name = name;
		}

		public string Country{ get; private set; }

		public string City{ get; private set; }

		public string Name{ get; private set; }

		public override string ToString ()
		{
			return string.Format ("[Hotel: Country={0}, City={1}, Name={2}]", Country, City, Name);
		}

	}

	public class Query
	{
		public Query (string country, string city)
		{
			Country = country;
			City = city;
		}

		public string Country{ get; private set; }

		public string City{ get; private set; }
	}

	public class Results
	{
		public Results (string country, string city, IEnumerable<Hotel> hotels)
		{
			Country = country;
			City = city;
			Hotels = hotels;
		}

		public string Country{ get; private set; }

		public string City{ get; private set; }

		public IEnumerable<Hotel> Hotels{ get; private set; }
	}

	public class AggregatorActor : ReceiveActor
	{

		private List<Hotel> Results;
		private int seen = 0;

		public AggregatorActor (ActorRef original, int waitFor)
		{

			Results = new List<Hotel> ();

			Receive<Results> (x => {
			
				if (++seen == waitFor) {
					original.Tell (x);

					Self.Tell (PoisonPill.Instance);
				}
			});

		}
	}

	public class CategoryActor : ReceiveActor
	{
		public CategoryActor (string country, IEnumerable<Hotel> hotels, bool top = false)
		{

			var listOfActors = new List<ActorRef> ();

			if (top) {
				var countries = hotels.Select (x => x.Country).Distinct ().ToList ();

				countries.ForEach (c => {
					var hotelsInCountry = hotels.Where (x => x.Country == c).ToList ();
					listOfActors.Add (Context.ActorOf (Props.Create<CategoryActor> (c, hotelsInCountry, false), c));
				});
			} else {
				var cities = hotels.Where (x => x.Country == country).Select (x => x.City).Distinct ().ToList ();
				cities.ForEach (city => {
					var hotelsInCity = hotels.Where (x => x.Country == country && x.City == city).ToList ();
					listOfActors.Add (Context.ActorOf (Props.Create<TopicActor> (country, city, hotelsInCity), city));
				});
			}

			Receive<Query> (q => {
				var sender = Sender;
				var aggregator = Context.ActorOf (Props.Create<AggregatorActor> (sender, listOfActors.Count), "Aggregator");
					
				listOfActors.ForEach (x => {
					x.Tell (q, aggregator);
				});
			});

		}
	}

	public class TopicActor : ReceiveActor
	{

		public TopicActor (string country, string city, IEnumerable<Hotel> hotels)
		{
			this.country = country;
			this.city = city;
			this.hotels = hotels;

			Receive<Query> (q => {
				var sender = Sender;

				sender.Tell (new Results (this.country, this.city, this.hotels.Where (x => x.Country == country && x.City == city).ToList ()));

			});
		}

		private string country;
		private string city;
		private IEnumerable<Hotel> hotels;
	}

	class MainClass
	{

		public static List<Hotel> GetHotels ()
		{
			var hotels = new List<Hotel> ();

			
			hotels.Add (new Hotel ("America", "NYC", "Hilton"));
			hotels.Add (new Hotel ("America", "NYC", "Plaza"));
			hotels.Add (new Hotel ("America", "NYC", "Pierre"));
			hotels.Add (new Hotel ("America", "Vegas", "Caesars"));
			hotels.Add (new Hotel ("America", "Vegas", "Mandalay"));
			hotels.Add (new Hotel ("America", "Vegas", "Belagio"));
			hotels.Add (new Hotel ("Australia", "Perth", "Burswood"));
			hotels.Add (new Hotel ("Australia", "Perth", "Hyatt"));
			hotels.Add (new Hotel ("Australia", "Perth", "Hilton"));
			hotels.Add (new Hotel ("Australia", "Perth", "Duxton"));
			hotels.Add (new Hotel ("Australia", "Perth", "Richardson"));
			return hotels;
		}

		public static void Main (string[] args)
		{
			using (var system = ActorSystem.Create ("System")) {


				var top = system.ActorOf (Props.Create<CategoryActor> (String.Empty, GetHotels (), true), "TopLevelCategory");

				Thread.Sleep (2300);

				var f = top.Ask<Results> (new Query ("America", "Vegas"));
				f.ContinueWith (x => {
					x.Result.Hotels.ToList ().ForEach (y => Console.WriteLine (y));
				});

				Console.ReadKey ();
				system.Shutdown ();
			}
		}


	}
}

Thanks rodger :)