using System;

using System.Linq;

using System.Collections.Generic;

​

public class Program

{

    public void Main()

    {

        var fooDataList = new List<Foo>();

        fooDataList.Add(new Foo { Bar = "Test1" });

        fooDataList.Add(new Foo { Bar = "Test2" });

        fooDataList.Add(new Foo { Bar = "Test3" });

        fooDataList.Add(new Foo { Bar = "Test4" });

        var fooList = new List<Foo>();

        var fooWithExtList = new List<Foo>();

        //assign foodata to fooList

        fooDataList.ForEach(fdl => fooList.Add(fdl));

        //assign foodata to fooWithExtList

        fooDataList.ForEach(fdl => fooWithExtList.Add(fdl));

        //set the fooWithExtList with extra info

        fooWithExtList.ForEach(fwel => fwel.Bar = fwel.Bar + "ext");

        //merge the list

        fooList = fooList.Concat(fooWithExtList).ToList();

        //print

        fooList.ForEach(fl => Console.WriteLine(fl.Bar));

    }

}

​

public class Foo

{

    public string Bar{get;set;}

}

​

​