using System;

using Newtonsoft.Json;

using Newtonsoft.Json.Linq;

​

public class Program

{

    public void Main()

    {

        var json = @"{ ""data"" : [

                       {""IsPlaceholder"": 0, ""Name"" : ""Test1"", ""Size"" : 2 },

                       {""IsPlaceholder"": 0, ""Name"" : ""Test2"", ""Size"" : 3 },

                       {""IsPlaceholder"": 0, ""Name"" : ""Test3"", ""Size"" : 1 }

                    ]}";

        var jsonD = JObject.Parse(json);

        var coolData = new JObject(jsonD);

        var placeholder = JObject.FromObject(new PlaceholderVm());

        var cnt = 0;

        var jObject = new JObject();

        JArray jArray = new JArray();

         foreach (JObject c in coolData["data"] as JArray)

        {

             jArray.Add(c);

​

            if (cnt % 2 == 0)

            {

                jArray[cnt].AddAfterSelf(placeholder);

            }

            cnt++;

        }

        jObject.Add("data", jArray);

        Console.WriteLine(jObject.ToString());

    }

}

​

public class PlaceholderVm

{

    public int IsPlaceholder = 1;

    public string Name = "Placeholder";

    public float Size { get; set; }

}