using System;

using System.Collections.Generic;

using System.Linq;

using Newtonsoft.Json.Linq;

public class Program

{

    public static void Main()

    {

        string json1 = @"

        {

            ""result"": [

            {

                ""sys_id"": ""11111111"",

                ""u_description"": ""test1""

            },

            {

                ""sys_id"": ""22222222"",

                ""u_description"": ""test2""

            }

            ]

        }";

​

        string json2 = @"

        {

            ""result"": [

            {

                ""sys_id"": ""11111111"",

                ""u_description"": ""test1""

            },

            {

                ""sys_id"": ""22222222"",

                ""u_description"": ""test2""

            },

            {

                ""sys_id"": ""33333333"",

                ""u_description"": ""test3""

            },

            {

                ""sys_id"": ""44444444"",

                ""u_description"": ""test4""

            }

            ]

        }";

​

​

        var firstJSON = JObject.Parse(json1);

        var secondJSON = JObject.Parse(json2);

​

        var sysIds = new HashSet<string>(firstJSON["result"].Select(jt => (string)jt["sys_id"]));

​

        foreach (var item in secondJSON["result"].ToList())

        {

            if (sysIds.Contains((string)item["sys_id"]))

            {

                item.Remove();

            }

        }

​

        foreach (var item in secondJSON["result"])

        {

            var sysId = (string)item["sys_id"];

            var desc = (string)item["u_description"];

​

            Console.WriteLine(sysId + " " + desc);

        }

​

        Console.WriteLine();

        Console.WriteLine(secondJSON.ToString());

    }

}