using System;

using System.Linq;

using System.Collections.Generic;

​

public class Program

{

    public class LastLogons

    {

        public int id { get; set; }

        public string SAMAccountName { get; set; }

        public DateTime lastLogon { get; set; }

    }

    public static void Main()

    {

        var InactiveList = new List<LastLogons>()

            {

                new LastLogons() { id = 1, SAMAccountName = "test.user1", lastLogon = DateTime.Now.AddDays(-10) },

                new LastLogons() { id = 1, SAMAccountName = "test.user1", lastLogon = DateTime.Now.AddDays(-100) },

                new LastLogons() { id = 2, SAMAccountName = "test.user2", lastLogon = DateTime.Now.AddDays(-100) },

                new LastLogons() { id = 2, SAMAccountName = "test.user2", lastLogon = DateTime.Now.AddDays(-1000) },

            };

​

            DateTime CurrentDate = DateTime.Now;

            int filterDays = 90;

​

            var result1 = InactiveList

                            .Where(l => l.lastLogon <= CurrentDate.AddDays(-filterDays))

                            .GroupBy(s => s.SAMAccountName)

                            .Select(scope => scope.OrderBy(l => l.lastLogon).Last())

                            .ToList();

​

            var result2 = InactiveList

                            .GroupBy(s => s.SAMAccountName)

                            .Select(scope => scope.OrderBy(l => l.lastLogon).Last())

                            .Where(l => l.lastLogon <= CurrentDate.AddDays(-filterDays))

                            .ToList();

​

            Console.WriteLine("Result count with old code - " + result1.Count());

            Console.WriteLine("Result count with new code - " + result2.Count());

    }

}