How to groupby JArray and show the max?

I have a JArray as below:

[
  {
    "group_pid": 1,
    "dataPool": 25000
  },
  {
    "group_pid": 0,
    "dataPool": 18750
  },
  {
    "group_pid": 1,
    "dataPool": 25000
  },
  {
    "group_pid": 1,
    "dataPool": 25000
  }
]

How to get the max value of the dataPool based on the group_pid?

from the example of the above JArray, I expect to get:

Expected result:

  [
      {
        "group_pid": 1,
        "dataPool": 25000
      },
      {
        "group_pid": 0,
        "dataPool": 18750
      }
   ]

I have tried the following, but I got compiler error CS0021, cannot apply indexing with []

JArray ja = (JArray)jaProjects.GroupBy(x => (long)x["group_pid"])
                .Select(x => (long)x["dataPool"]);

You’re only selecting "dataPool" directly without accounting for how you’ll pick the maximum value within each group_pid. Try using OrderByDescending and First or a nested Select to access each item in the grouped collections:

using System;
using System.Linq;
using Newtonsoft.Json.Linq;

public class Program
{
    public static void Main()
    {
        string json = @"
        [
            { ""group_pid"": 1, ""dataPool"": 25000 },
            { ""group_pid"": 0, ""dataPool"": 18750 },
            { ""group_pid"": 1, ""dataPool"": 25000 },
            { ""group_pid"": 1, ""dataPool"": 25000 }
        ]";
        JArray jsonArray = JArray.Parse(json);
        var result = new JArray(
            jsonArray
                .GroupBy(item => (int)item["group_pid"])
                .Select(group => group
                    .OrderByDescending(item => (int)item["dataPool"])
                    .First())
        );
        Console.WriteLine(result.ToString());
    }
}

Output:

[
  {
    "group_pid": 1,
    "dataPool": 25000
  },
  {
    "group_pid": 0,
    "dataPool": 18750
  }
]

Try on dotnetfiddle.net