using System;

using System.Collections;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Diagnostics;

using System.IO;

using System.Reflection;

​

using Newtonsoft.Json;

using Newtonsoft.Json.Linq;

using Newtonsoft.Json.Converters;

using Newtonsoft.Json.Serialization;

​

​

    // https://stackoverflow.com/questions/41171017/how-to-get-the-key-from-json-object-and-convert-into-an-array

​

​

    public class Program

    {

        public static void Main()

        {

            var jsonString = @"{

                 ""Date"": ""2016-12-15"",

                 ""Data"": {

                   ""A"": 4.4023,

                   ""AB"": 1.6403,

                   ""ABC"": 2.3457

                 }

            }";

​

            var root = JToken.Parse(jsonString);

​

            var properties = root

                // Select nested Data object

                .SelectTokens("Data")

                // Iterate through its children, return property names.

                .SelectMany(t => t.Children().OfType<JProperty>().Select(p => p.Name))

                .ToArray();

​

            Console.WriteLine(String.Join(",", properties)); // Prints A,AB,ABC

        }

    }