Question

我的数据结构如下所示。对于每个（人，游戏）对，我需要找到过去24小时内的最新分数。在LINQ中可以这样做吗？像（人物，游戏，最新分数）

的东西

+----------------+-----------------+---------------+-+------------+
| Person         |  Game           | Score         |EventTime     |
+-----------------------------------------------------------------+
|                |                 |               |              |
|                |                 |               |              |
+----------------+-----------------+---------------+--------------+

任何提示都会非常有用。

Answer 1

假设您有这样的课程：

    class GameInfo
    {

        public DateTime EventTime { get; set; }
        public String Game { get; set; }
        public String Person { get; set; }
        public double Score { get; set; }
    }

你可以这样做：

        List<GameInfo> data = new List<GameInfo> { 
        new GameInfo { Game = "G1", Person = "A", Score = 10, EventTime = new DateTime(2014, 10, 10, 10, 10, 10) },
        new GameInfo { Game = "G1", Person = "A", Score = 10, EventTime = new DateTime(2014, 10, 10, 10, 10, 10) },
        new GameInfo { Game = "G2", Person = "B", Score = 11, EventTime = new DateTime(2014, 10, 10, 20, 10, 10) },
        new GameInfo { Game = "G2", Person = "B", Score = 11, EventTime = new DateTime(2014, 10, 10, 20, 10, 10) }
    };

        var q = from game in data
                group game by new { G = game.Game, P = game.Person } into g

                select new {
                    Person = g.Key.P,
                    Game = g.Key.G,
                    Score = g.Aggregate((curmin, x) => (curmin == null || (x.EventTime) < curmin.EventTime ? x : curmin)).Score
                };

        foreach (var item in q)
        {
            Console.WriteLine("{0}, {1}, {2}", item.Game, item.Person, item.Score);
        }

正如@Rawling指出的那样，如果你拥有大量数据集，那么获取scoce可能会非常昂贵。因此，有效地执行此操作可能会节省大量时间来获得所需的输出。

Answer 2

var dt = DateTime.Now.AddDays(-1);
var results = context.Where(x=>x.EventTime >= dt)
    .GroupBy(x=>new {x.Person,x.Game})
    .Select(x=>new 
    {
        x.Key.Person,
        x.Key.Game,
        LatestScore = x.Where(d=>d.EventTime == x.Max(l=>l.EventTime))
                       .Select(d=>d.Score)
                       .FirstOrDefault()
    });

Linq查询做分组和分钟

2 个答案: