using System;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        var myList = new[] {

            new { id = 1, price = 30},

            new { id = 2, price = 20},

            new { id = 3, price = 40},

            new { id = 3, price = 60},

            new { id = 1, price = 70},

            new { id = 1, price = 20},

            new { id = 2, price = 110},

        };

​

        var result = myList.GroupBy(x => x.id).Select(x => new { id = x.Key, price = x.Sum(y => y.price)  });

        foreach(var item in result)

        {

            Console.WriteLine(string.Format("id:{0}, priceSum:{1}", item.id, item.price));  

        }

    }

}