LINQ 将列的总和添加到列表条目

Posted 2023-02-16

【中文标题】LINQ 将列的总和添加到列表条目

【英文标题】：LINQ add sum of columns to list entry

【发布时间】：2021-07-16 10:33:59

【问题描述】：

我目前正在开发一个 .net 5.0 应用程序。

我需要使用 LINQ 来做一个复杂的查询：

给出的是List<Player> 我需要转换List<Player>，但保留所有条目 将每支球队的 TotalScore 添加到“SerieA”中的所有球员

不幸的是，我不知道如何使用 C# LINQ 扩展方法语法正确计算联盟中所有球员的每支球队的 TotalScore。

播放器类：

public class Player

    public string Name  get; set; 
    public string Team   get; set; 
    public int Score   get; set; 
    public string League   get; set; 
    public int TotalTeamScore   get; set; 

程序类

public class Program

    public static void Main()
    
        // given is a List<Player> - I need to calculate the TotalScore for each team ONLY for Leage "SerieA"
        var players = new List<Player> 
            new Player  Name = "Alex", Team = "A", Score = 10, League = "SerieA", TotalTeamScore = 0 ,
            new Player  Name = "Anna", Team = "A", Score = 20, League = "SerieA", TotalTeamScore = 0 ,
            new Player  Name = "Berta", Team = "B", Score = 60, League = "SerieA", TotalTeamScore = 0 ,
            new Player  Name = "Benny", Team = "B", Score = 40, League = "SerieA", TotalTeamScore = 0 ,
            new Player  Name = "Charlie", Team = "C", Score = 40, League = "PremierLeague", TotalTeamScore = 0 ,
            new Player  Name = "Connor", Team = "C", Score = 40, League = "PremierLeague", TotalTeamScore = 0 ,
        ;

        // I need to find a proper way to calculate the TotalTeamScore for each Team in league SerieA and add this score to the players...
        var teamTotalScores = players
                                .Where(p => p.League == "SerieA")
                                .GroupBy(p => p.Team)
                                .Select(p => new Player 
                                    TotalTeamScore = p.Sum(s => s.Score)
                                    // Score = x.Key ??
                                )
                                .ToList();
        
// desired result: same List<Player> - only the Total TeamScore of a Team in "SerieA" should be calculated for each team and added to each player in a team:
// new Player  Name = "Alex", Team = "A", Score = 10, League = "SerieA", TotalTeamScore = 30 ,
// new Player  Name = "Anna", Team = "A", Score = 20, League = "SerieA", TotalTeamScore = 30 ,
// new Player  Name = "Luke", Team = "B", Score = 60, League = "SerieA", TotalTeamScore = 100 ,
// new Player  Name = "Lucy", Team = "B", Score = 40, League = "SerieA", TotalTeamScore = 100 ,
        
// new Player  Name = "Charlie", Team = "C", Score = 40, League = "PremierLeague", TotalTeamScore = 0 ,
// new Player  Name = "Connor", Team = "C", Score = 40, League = "PremierLeague", TotalTeamScore = 0 ,
    

你知道如何解决这个问题吗？

您知道如何使用 C# LINQ 扩展方法语法正确计算联盟中所有球员的每支球队的 TotalScore。

【参考方案1】：

LINQ 专为查询而设计，而您需要修改集合中的对象。

虽然您可以使用 Enumerable.Select 执行此操作，但标准的 foreach 循环会更合适：

var serieAPlayers = players.Where(p => p.League == "SerieA");

var teamScores = serieAPlayers
    .GroupBy(p => p.Team)
    .ToDictionary(grp => grp.Key, grp => grp.Sum(p => p.Score));

foreach (var player in serieAPlayers) player.TotalTeamScore = teamScores[player.Team];

【讨论】：

谢谢，效果很好！！也许有一点改进，我必须检查字典中是否存在键 [player.Team]。 :)

啊，是的，foreach 应该只迭代意甲的球员；我会更新答案。