using System;

using System.Collections;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Data;

using System.IO;

​

using Newtonsoft.Json;

using Newtonsoft.Json.Linq;

using Newtonsoft.Json.Converters;

using Newtonsoft.Json.Serialization;    

​

using NUnit.Framework; // Throws NUnit.Framework.AssertionException

​

//https://stackoverflow.com/questions/77614687/convert-jarray-to-list-keeping-only-one-nested-jtoken

​

    class TestClass

    {

        public static void Test()

        {

            var json = 

                """

                [     

                     {

                        "1": "A",

                        "2": "B",

                        "3": {

                                  "KeyICareAbout": "C",

                                  "5": "D"

                             }    

​

                     },     

                     {

                        "1": "E",

                        "2": "F",

                        "3": {

                                  "KeyICareAbout": /* Some comment */ "G",

                                  "5": "H"

                             }    

​

                     }

                ]

                """;

            var fileName = "Question77614687.json";

            File.WriteAllText(fileName, json);

            var key = "KeyICareAbout";

            using var stream = File.OpenRead(fileName);

            using var textReader = new StreamReader(stream, Encoding.UTF8);

            using var reader = new JsonTextReader(textReader);

            var list = new List<JToken>();

            while (reader.Read())

            {

                if (reader.TokenType == JsonToken.PropertyName && (string)reader.Value == key)

                {

                    list.Add(JToken.Load(reader.ReadToContentAndAssert()));

                }

            }

            Console.WriteLine(JsonConvert.SerializeObject(list, Formatting.Indented));

            Assert.That(list.Select(i => i.ToString()).SequenceEqual(new [] { "C", "G" }));

            File.Delete(fileName);

        }   

    }

​

    public static partial class JsonExtensions

    {

        public static JsonReader AssertTokenType(this JsonReader reader, JsonToken tokenType) => 

            reader.TokenType == tokenType ? reader : throw new JsonSerializationException(string.Format("Unexpected token {0}, expected {1}", reader.TokenType, tokenType));

        public static JsonReader ReadToContentAndAssert(this JsonReader reader) =>

            reader.ReadAndAssert().MoveToContentAndAssert();

​

        public static JsonReader MoveToContentAndAssert(this JsonReader reader)

        {

            ArgumentNullException.ThrowIfNull(reader);

            if (reader.TokenType == JsonToken.None)       // Skip past beginning of stream.

                reader.ReadAndAssert();

            while (reader.TokenType == JsonToken.Comment) // Skip past comments.

                reader.ReadAndAssert();

            return reader;

        }

​

        public static JsonReader ReadAndAssert(this JsonReader reader)

        {

            ArgumentNullException.ThrowIfNull(reader);

            if (!reader.Read())

                throw new JsonReaderException("Unexpected end of JSON stream.");

            return reader;

        }

    }

​

    public class Program

    {

        public static void Main()

        {

            Console.WriteLine("Environment version: {0} ({1}), {2}", System.Runtime.InteropServices.RuntimeInformation.FrameworkDescription , Environment.Version, Environment.OSVersion);

            Console.WriteLine("{0} version: {1}", typeof(JsonSerializer).Namespace, typeof(JsonSerializer).Assembly.FullName);

            Console.WriteLine();

​

            try

            {

                TestClass.Test();

            }

            catch (Exception ex)

            {

                Console.WriteLine("Failed with unhandled exception: ");

                Console.WriteLine(ex);

                throw;

            }

        }

    }

​