C LINQ de Duplication & de duplication sum

Linq Three ways of weight removal

class Program
    {
    
        static void Main(string[] args)
        {
    
            Console.WriteLine("Hello World!");
            
            List<_model> _list = new List<_model>();
            _list.Add(new _model() {
     _sum = 1, _id = 1, _int = 1 });
            _list.Add(new _model() {
     _sum = 3, _id = 1, _int = 2 });
            _list.Add(new _model() {
     _sum = 7, _id = 2, _int = 1 });
            _list.Add(new _model() {
     _sum = 2, _id = 3, _int = 1 });
            _list.Add(new _model() {
     _sum = 4, _id = 3, _int = 2 });
            _list.Add(new _model() {
     _sum = 9, _id = 3, _int = 3 });

            // Returns a list of 
            var _list1 = _list.GroupBy(i => i._id).Select(i => i.OrderByDescending(i => i._int).First()).ToList();
            foreach (var item in _list1)
            {
    
                Console.WriteLine(item._sum);
                Console.WriteLine(item._id);
                Console.WriteLine(item._int);
            }

            // Return summation ( Single condition sort )
            var _list2 = _list.GroupBy(i => i._id).Select(i => new {
     i.Key, _sum = i.Sum(o=>o._sum) }).ToList();
            foreach (var item in _list2)
            {
    
                Console.WriteLine(item.Key);
                Console.WriteLine(item._sum);
            }

            // Return summation ( Multiple conditional sorting )
            var _list3 = _list.GroupBy(i => new {
     i._id,i._int}).Select(i => new {
     i.Key, _sum = i.Sum(o => o._sum) }).ToList();
            foreach (var item in _list3)
            {
    
                Console.WriteLine(item.Key._id);
                Console.WriteLine(item.Key._int);
                Console.WriteLine(item._sum);
            }

            //===========================================================================
            Console.ReadKey();
        }

        public class _model
        {
    
            public int _sum {
     get; set; }
            public int _id {
     get; set; }
            public int _int {
     get; set; }
        }
    }