using System.Linq;

using System.Collections.Generic;

using System;

public class Program

{

    public static void Main()

    {

        var seed = new Random();

        int range = 20;

        var As = Enumerable.Range(0,range).Select(i => new A { Name = "Name" + i, Number = seed.Next(range) }).ToList();

        var Bs = Enumerable.Range(0,range).Select(i => new B { Place = "Place" + i, Number = seed.Next(range) }).ToList();

        var abs = new Dictionary<int,List<Tuple<A,B>>>();

        foreach(var a in As)

        {

            if(!abs.ContainsKey(a.Number))

            {

                abs[a.Number] = new List<Tuple<A,B>>();

            }

            abs[a.Number].Add(new Tuple<A,B>(a,null));

        }

        foreach(var b in Bs)

        {

            if(!abs.ContainsKey(b.Number))

            {

                abs[b.Number] = new List<Tuple<A,B>>();

            }

            abs[b.Number].Add(new Tuple<A,B>(null,b));

        }

        foreach(var lt in abs.OrderByDescending( k => k.Key ))

        {

            foreach(var tuple in lt.Value.Where(t => t.Item1 != null))

            {

                var a = tuple.Item1;

                Console.WriteLine(a.Name + ", " + a.Number);

            }

            foreach(var tuple in lt.Value.Where(t => t.Item2 != null))

            {

                var b = tuple.Item2;

                Console.WriteLine(b.Place + ", " + b.Number);

            }

        }

    }

}

​

public class A

{

    public string Name { get; set; }

    public int Number { get; set; }

}

​

public class B

{

    public string Place { get; set; }

    public int Number { get; set; }

}

​

​