using System;

using System.Collections;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Linq.Expressions;

​

public class Program

{

    public static void Main()

    {

        var k1 = new List<int>(){1,2,3,4,5};

        var k2 = new List<int>(){1,2,3,4,5};

        var o1 = new A(){k=k1, objectName="o1"};

        var o2 = new A(){k=k2, objectName="o2"};

        var l = new List<A>();

        l.Add(o1);

        l.Add(o2);

        var b = l.GroupBy(a => a.k, new ListComparer<int>())

                 .Select(g => new 

                    {

                        Key = String.Join(",", g.Key.Select(i => i)), 

                        n = String.Join(",",g.Select(i => i.objectName))

                    });

        foreach(var item in b)

        {

            Console.WriteLine(string.Format("{0} : {1}", item.Key, item.n));

        }

    }

    public class A

    {

        public List<int> k;

        public string objectName;

    }

    public class ListComparer<T> : IEqualityComparer<List<T>>

    {

        public bool Equals(List<T> left, List<T> right)

        {

            return left.OrderBy(i => i).SequenceEqual(right.OrderBy(i => i));

        }

        public int GetHashCode(List<T> list)

        {

            return list.Count;

        }

    }

}