using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        // Two dimensional list of ints

            var arr = new List<List<int>>();

            var rand = new Random();

​

            // fill the array with random values, this works fine.

            for (int i = 0; i < 10; i++)

            {

                arr.Add(new List<int>());

                for (int k = 0; k < 5; k++)

                {

                    arr[i].Add(rand.Next(1, 21));

                }

            }

​

            var q = from e in arr select e;

            List<int> lst = q.SelectMany(d => d).ToList();  // This fails with InvalidCastException

​

            // here I would like to pretend that the list is one dimensional

            foreach (int i in lst)

            {

                Console.WriteLine(i);

            }

    }

}