[C#] LINQ(Language-Integrated Query) 2

using System.Security.Cryptography;

namespace Study
{
    class Program
    {
        public enum ClassType
        {
            Knight,
            Archer,
            Mage
        }

        public class Player
        {
            public ClassType ClassType;
            public int Level;
            public int Hp;
            public int Attack;
            public List<int> Items = new List<int>();
        }

        static List<Player> _players = new List<Player>();

        static void Main(string[] args)
        {
            Random rand = new Random();

            for (int i = 0; i < 100; ++i)
            {
                Player player =
                new Player()
                {
                    ClassType = (ClassType)rand.Next(0, 3),
                    Level = rand.Next(0, 100),
                    Hp = rand.Next(100, 1000),
                    Attack = rand.Next(50, 100),
                };

                for (int j = 0; j < 5; ++j) { player.Items.Add(rand.Next(1, 101)); }

                _players.Add(player);
            }

            //Q. 모든 아이템 목록을 추출
            {
                var playerItems =   from p in _players
                                    from i in p.Items
                                    where i < 30
                                    select new { p, i };

                var li = playerItems.ToList();

                foreach (var info in li)
                {
                    Console.WriteLine($"{info.i} {info.p.ClassType}");
                }
            }

            //Grouping
            {
                var playerByLevel = from p in _players
                                    group p by p.Level into g
                                    orderby g.Key
                                    select new { g.Key, players = g };

                foreach (var player in playerByLevel)
                {
                    Console.WriteLine($"Group by level: {player.Key}");

                    foreach(Player p in player.players)
                    {
                        Console.WriteLine($"\t\tLEVEL:{p.Level}, HP:{p.Hp}, TYPE:{p.ClassType}");
                    }

                    Console.WriteLine();
                }
            }

            //Join
            {
                List<int> levels = new List<int>() { 1, 5 ,10 };

                var playerLevels = from p in _players
                                   join l in levels
                                   on p.Level equals l
                                   select p;

                foreach(Player player in playerLevels)
                {
                    Console.WriteLine($"LEVEL:{player.Level}, HP:{player.Hp}, TYPE:{player.ClassType}");
                }
            }
        }
    }
}

 

· 중첩 from

var playerItems =   from p in _players
                    from i in p.Items
                    where i < 30
                    select new { p, i };

var li = playerItems.ToList();

foreach (var info in li)
{
    Console.WriteLine($"{info.i} {info.p.ClassType}");
}

• from을 중첩하여 사용할 수 있습니다. List<Player>인 _player에 있는 p.Item에 접근하여 사용한 예제입니다.

 

 

· grouping

var playerByLevel = from p in _players
                    group p by p.Level into g
                    orderby g.Key
                    select new { g.Key, players = g };

foreach (var player in playerByLevel)
{
    Console.WriteLine($"Group by level: {player.Key}");

    foreach(Player p in player.players)
    {
        Console.WriteLine($"\t\tLEVEL:{p.Level}, HP:{p.Hp}, TYPE:{p.ClassType}");
    }

    Console.WriteLine();
}

• _players에 있는 리스트 중 특정한 요소끼리 그룹을 지어 리턴할 수 있습니다.

 

 

· join

List<int> levels = new List<int>() { 1, 5 ,10 };

var playerLevels = from p in _players
                   join l in levels
                   on p.Level equals l
                   select p;

foreach(Player player in playerLevels)
{
    Console.WriteLine($"LEVEL:{player.Level}, HP:{player.Hp}, TYPE:{player.ClassType}");
}

• 두개의 리스트에서 공통되는것끼리 조인하여 리턴할 수 있습니다.