gistfile1.cs

using System;
using System.Linq;
using System.IO;

class MainClass
{
	public static void Main (string[] args)
	{
		var items = File.ReadLines("textfile.txt")
                        .Select(x=>x.Split(' '))
			.GroupBy(x=>x[1], x=>long.Parse(x[0]))
			.Select(x=>new { x.Key, Value=x.Skip(1).Zip(x, (a,b)=> a-b) });
		
		foreach (var item in items)
			Console.WriteLine("{0}:{1}", item.Key, String.Join(",", item.Value.ToArray()));

	}
}

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