using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var data = new[]

                {

                    new { Col1 = "A", Col2 = "X", Value = 10 },

                    new { Col1 = "A", Col2 = "Z", Value = 15 },

                    new { Col1 = "B", Col2 = "X", Value = 9 },

                    new { Col1 = "B", Col2 = "Y", Value = 12 },

                    new { Col1 = "B", Col2 = "Z", Value = 6 },

                };

​

​

            int maxCount = 0;

            var result = data.GroupBy(x => x.Col2)

                               .OrderByDescending(x => x.Count())

                               .Select(x => 

                                   {

                                       if (maxCount == 0)

                                           maxCount = x.Count();

                                       var Value = x.Select(z => z.Value);

                                       return new 

                                       {

                                           name = x.Key,

                                           data = maxCount == x.Count() ? Value.ToArray() : Value.Concat(new int[maxCount - Value.Count()]).ToArray()

                                       };

                                   });

​

            foreach (var item in result)

            {

                Console.WriteLine("Name: {0}", item.name);

                foreach (int dat in item.data)

                {

                    Console.WriteLine("Data: {0}", dat);

                }

                Console.WriteLine();

            }

    }

}