using System;

using System.Linq;

​

public class Program

{

​

    public static void Main(string[] args)

    {

        var x = new string[] { "a", "a", "a", "b", "a", "a", "c" };

​

​

        int groupId = -1;

        var result = x.Select((s, i) => new

        {

            value = s,

            groupId = (i > 0 && x[i - 1] == s) ? groupId : ++groupId

        }

        ).GroupBy(u => new { groupId });

​

​

        foreach (var item in result)

        {

            Console.WriteLine(item.Key);

            foreach (var inner in item)

            {

                Console.WriteLine(" => " + inner.value);

            }

        }

    }

​

}