using System;
using System.Collections.Generic;
using System.Linq;

class LinqGroupDemo
{
    static public void Main(string[] args)
    {
        var query =
            from column in GetSource()
            group column by new {column.LocId, column.SecId} into g
            orderby g.Key.LocId, g.Key.SecId
            select new
            {
                LocId = g.Key.LocId,
                SecId = g.Key.SecId,
                Columns = g
            };

        foreach (var key in query)
        {
            Console.WriteLine("LocId:{0}, SecId:{1}",
                              key.LocId,
                              key.SecId);

            foreach (var column in key.Columns)
            {
                Console.WriteLine("  StartElevation:{0}, EndElevation:{1}",
                                  column.StartElevation,
                                  column.EndElevation);
            }
        }
    }

    static private List<Column> GetSource()
    {
        return new List<Column>
        {
            new Column { LocId = 1 , SecId = 1, StartElevation = 0, EndElevation = 160 },
            new Column { LocId = 1 , SecId = 1, StartElevation = 160, EndElevation = 320 },
            new Column { LocId = 1 , SecId = 2, StartElevation = 320, EndElevation = 640 },
            new Column { LocId = 2 , SecId = 1, StartElevation = 0, EndElevation = 160 },
            new Column { LocId = 2 , SecId = 2, StartElevation = 160, EndElevation = 320 }
        };
    }
}

public class Column
{
    public int LocId { get; set; }
    public int SecId { get; set; }
    public double StartElevation { get; set; }
    public double EndElevation { get; set; }
}