using System;

using Newtonsoft.Json;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var originalList  = new List<string[]> {new string[]{"a","c"}, new string[]{"s","b"}, new string[]{"a","b"},new string[]{"a","b"}, new string[]{"a","b"}, new string[]{"a","b"}};

        List<string> outputList = new List<string>();

        originalList.ForEach(f => outputList.Add(string.Join(",", f)));

        var query = outputList.GroupBy(x => x)

              .Where(g => g.Count() > 1)

              .Select(y => new { Element = y.Key, Counter = y.Count() })

              .ToList();

        foreach(var a in query){

        Console.WriteLine(string.Join("\n", a.Counter));

        }

​

    }

}