using System;

using System.Collections.Generic;

using System.Dynamic;

using System.Linq;

using System.Text.Json;

public class Program

{

  public static void Main()

  {

    var results = Data.GetData(); //query result

​

    var resultsV2 = results.GroupBy(r => r.Gender);

    var list = new List<IDictionary<string, object>>();

​

    foreach(var g in resultsV2)

    {

      IDictionary<string, object> obj = new ExpandoObject();

​

      var data = g.Select(x => x);

      obj["Gender"] = $"{g.Key}";

​

      foreach(var d in data)

      {

        var propName = $"{d.Age}";

        obj[propName] = $"{d.Value}";

      }

​

      list.Add(obj);

    }

​

    string jsonString = JsonSerializer.Serialize(list);

​

    Console.WriteLine(jsonString);

   }

  public class Data

  {

    public string Gender { get; set; }

    public int Age { get; set; }

    public int Value { get; set; }

​

    public static List<Data> GetData()

    {

      return new List<Data>

      {

        new Data() { Gender = "Male", Age = 20, Value = 5 },

        new Data() { Gender = "Male", Age = 30, Value = 3 },

        new Data() { Gender = "Female", Age = 20, Value = 9 }

      };

    }

  }

}