using System;

using Newtonsoft.Json;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Hello World");

        List<File> list = new List<File>();

        list.Add(new File("file1", "1", DateTime.Parse("2021-01-01")));

        list.Add(new File("file2", "1", DateTime.Parse("2021-01-08")));

        list.Add(new File("file3", "2", DateTime.Parse("2021-01-01")));

        list.Add(new File("file1", "3", DateTime.Parse("2021-01-01")));

        list.Add(new File("file2", "3", DateTime.Parse("2021-01-08")));

        list.Add(new File("file3", "4", DateTime.Parse("2021-01-08")));

        //list.Dump();

​

        var results = from l in list

                      group l by l.identifier into g

                      //select g;

                      select new { Id = g.Key, Files = g.ToList() };

​

        //results.Dump();

​

        var set2 = results.Where( x => x.Files.Count == 1).Select( y => y.Files.First()).ToList();

        //set2.Dump();

        var set3 = results.Where( x => x.Files.Count > 1);

        //set3.Dump();

        var set4 = set3.Select( x => x.Files.OrderByDescending( y => y.fileDate ).First());

        //set4.Dump();

        foreach (var i in set4)

        {

        //  set2.Add(i);

        }

        set2.AddRange(set4);

​

        // original list

        list.Dump();

​

        // filtered list

        set2.Dump();

​

        var excludeList = list.Except(set2);

​

        // removed list

        excludeList.Dump();

    }

}

​

public class File {

    public File(string name, string id,DateTime date)

    {

        this.name = name;

        this.identifier = id;

        this.fileDate = date;

    }

    public string name {get;set;}

    public string identifier {get;set;}

    public DateTime fileDate {get;set;}

}

​

public static class Dumper

{

    public static string ToPrettyString(this object value)

    {

         return JsonConvert.SerializeObject(value, Formatting.Indented);

    }

​

    public static T Dump<T>(this T value)

    {

        Console.WriteLine(value.ToPrettyString());

        return value;

    }

}