C# LINQ 使用 DISTINCT 计数元素

Posted 2023-03-04

【中文标题】C# LINQ 使用 DISTINCT 计数元素

【英文标题】：C# LINQ counting elements with DISTINCT

【发布时间】：2013-07-13 04:52:23

【问题描述】：

我有一个 KeyValuePair 项的集合，其中 DateTime 为键，字符串为值。 基本上我的数据看起来像：

12/07/2013 - 10220
12/07/2013 - 10220
12/07/2013 - 12220
12/07/2013 - 11240
12/07/2013 - 15220
13/07/2013 - 23220
13/07/2013 - 35620
14/07/2013 - 15620
14/07/2013 - 15620

我想要一份我每天有多少物品（不同）的清单。所以查询将导致：

12/07/2013 - 4
13/07/2013 - 2
14/07/2013 - 1

【参考方案1】：

以下是完整示例的解决方案

        var list = new[]
        
            new Date = new DateTime(2013,07,12), value = 10220,
            new Date = new DateTime(2013,07,12), value = 10220,
            new Date = new DateTime(2013,07,12), value = 12220,
            new Date = new DateTime(2013,07,12), value = 11240,
            new Date = new DateTime(2013,07,12), value = 15220,
            new Date = new DateTime(2013,07,13), value = 23220,
            new Date = new DateTime(2013,07,13), value = 35620,
            new Date = new DateTime(2013,07,14), value = 15620,
            new Date = new DateTime(2013,07,14), value = 15620,
        ;


        var res = from l in list group l by new  l.Date  into g select new  g.Key.Date, value = g.Distinct().Count() ;

        foreach (var item in res)
        
            Console.WriteLine(item.Date + " " + item.value);
        

【参考方案2】：

使用group by

var dateGrouped = dates.GroupBy(x => x.Key)
                       .Select(x => new  Date = x.Key, Values = x.Distinct().Count() );