ienumerable 相关问题

我简化了我的问题公开课申请 { 公共 int Id { 得到;放; } 公共 int 版本 { 获取;放; } 公共 int 状态 { 获取;放; } } 我的 3 个清单： IE可枚举我简化了我的问题 public class Application { public int Id { get; set; } public int Version { get; set; } public int Status { get; set; } } 我的 3 个清单： IEnumerable<Application> applications1 = new List<Application> { new Application {Id = 1, Version = 1, Status = 1}, new Application {Id = 2, Version = 1, Status = 1}, new Application {Id = 3, Version = 3, Status = 1} }; IEnumerable<Application> applications2 = new List<Application> { new Application {Id = 1, Version = 2, Status = 2}, new Application {Id = 2, Version = 2, Status = 2}, new Application {Id = 3, Version = 1, Status = 0} }; IEnumerable<Application> applications3 = new List<Application> { new Application {Id = 1, Version = 5, Status = 1}, new Application {Id = 2, Version = 0, Status = 1}, new Application {Id = 3, Version = 6, Status = 1} }; 我想制作这个： IEnumerable<Application> applications4 = new List<Application> { new Application {Id = 1, Version = 5, Status = 2}, new Application {Id = 2, Version = 2, Status = 2}, new Application {Id = 3, Version = 6, Status = 1} }; 即具有最高版本和状态值的列表。我尝试过 LINQ 但我不明白。我最好的是这个，但它只是获得了最高版本。我不明白当有 2 个属性可供选择时我该怎么做： IEnumerable<Application> applications4 = applications1 .Concat(applications2) .Concat(applications3) .GroupBy(a => a.Id) .Select(g => g.Aggregate((acc, curr) => acc.Version > curr.Version ? acc: curr )) .ToList(); 您应该使用 Max() 从分组属性中获取最大值。 IEnumerable<Application> applications4 = applications1 .Concat(applications2) .Concat(applications3) .GroupBy(a => a.Id) .Select(g => new Application { Id = g.Key, Version = g.Max(x => x.Version), Status = g.Max(x => x.Status) }) .ToList(); 您的问题忽略了一个非常重要的点 - 哪个属性（版本或状态）更重要？我假设版本更重要，并创建了一个自定义比较器来对结果进行排序。基本上我想要的是按应用程序 ID 对项目进行group，然后获得最高的结果。我使用自定义比较器来获取它。如果您不想使用比较器，可以随时将其更改为： .Select(x => x.OrderByDescending(x => x.Version).ThenBy(x => x.Status).First()); internal class Program { static async Task Main(string[] args) { IEnumerable<Application> applications1 = new List<Application> { new Application {Id = 1, Version = 1, Status = 1}, new Application {Id = 2, Version = 1, Status = 1}, new Application {Id = 3, Version = 3, Status = 1} }; IEnumerable<Application> applications2 = new List<Application> { new Application {Id = 1, Version = 2, Status = 2}, new Application {Id = 2, Version = 2, Status = 2}, new Application {Id = 3, Version = 1, Status = 0} }; IEnumerable<Application> applications3 = new List<Application> { new Application {Id = 1, Version = 5, Status = 1}, new Application {Id = 2, Version = 0, Status = 1}, new Application {Id = 3, Version = 6, Status = 1} }; // you can use OrderByDescending().First() for applications using EF lower than 6.0.0 var applications4 = applications1.Union(applications2).Union(applications3) .GroupBy(x => x.Id) .Select(x => x.MaxBy(x => x, new VersionStatusComparer())); foreach (var item in applications4) { Console.WriteLine("Id: {0} Version: {1} Status: {2}", item.Id, item.Version, item.Status); } } } internal class VersionStatusComparer : IComparer<Application> { public int Compare(Application? x, Application? y) { var versionResult = CompareVersion(x.Version, y.Version); if (versionResult == 0) { return CompareStatus(x.Status, y.Status); } return versionResult; } private int CompareVersion(int xVersion, int yVersion) { if (xVersion > yVersion) { return 1; } else if (xVersion < yVersion) { return -1; } return 0; } private int CompareStatus(int xStatus, int yStatus) { if (xStatus > yStatus) { return 1; } else if (xStatus < yStatus) { return -1; } return 0; } } } 这是一种更面向 OOP 的方法，但我希望它看起来更明确。如果您需要更复杂的场景，您可以更新 Merge 逻辑。它具有 O(n) 复杂度（n 个元素的数组需要 n 个“陡峭”才能完成）并使用字典： public class Application { public int Id { get; set; } public int Version { get; set; } public int Status { get; set; } public bool Merge(Application app){ if(app.Id != Id) return false; this.Version = Math.Max(app.Version, this.Version); this.Status = Math.Max(app.Status, this.Status); return true; } } //... IEnumerable<Application> applications4 = new List<Application>(); Dictionary<int,Application> res = new Dictionary<int,Application>(); foreach( var app in applications1.Concat(applications2).Concat(applications3) ){ // existing value, then update if( res.TryGetValue( app.Id, out Application appToProceed )) appToProceed.Merge(app); // new id value, then add else res.Add(app.Id,app); } // applications4 = res.Values.ToList(); 关于基准测试结果，它是关于 ns 的，所以只是作为信息： | Method | Mean | Error | StdDev | Gen0 | Allocated | |---------------------------------------------- |-----------:|--------:|--------:|-------:|----------:| | Benchmark_Using_Dictionary__3List_1000Element | 226.8 ns | 3.03 ns | 2.84 ns | 0.0780 | 408 B | | Benchmark_Using_LINQ__3List_1000Element | 299.7 ns | 4.04 ns | 3.59 ns | 0.1040 | 544 B | | Benchmark_Using_Dictionary__3List_3Element | 652.5 ns | 2.09 ns | 1.85 ns | 0.1125 | 592 B | | Benchmark_Using_LINQ__3List_3Element | 1,631.4 ns | 8.12 ns | 7.59 ns | 0.2842 | 1488 B | （3List 表示 app1 + app2 + app3 和 1000Element 表示每个应用程序有 1000 个 id 可以使用）

c# linq merge ienumerable

回答 3 投票 0

将 3 个 IEnumerable<customObj>“列表”合并为 1 个 IEnumerable<customObj>

我简化了我的问题自定义对象公开课申请 { 公共 int Id { 得到;放; } 公共 int 版本 { 获取;放; } 公共 int 状态 { 获取;放; } } 我的 3 个“列表&q...

c# linq ienumerable

回答 2 投票 0

嗨，如何在 IEnumerable<> 列表上使用 foreach？

public IEnumerable 合并（IEnumerable 第一，IEnumerable 第二） { }

ienumerable

回答 1 投票 0

如何测试 IEnumerable.GetEnumerator() 方法？

假设我有一个生成斐波那契数的类：公共类斐波那契数列：IEnumerable { 公共 IEnumerator GetEnumerator() { ...