使用C# LINQ计算具有DISTINCT特性的元素个数。

Question

我有一组键值对项目，键为 DateTime 类型，值为字符串类型。基本上我的数据长这样：

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

我希望能够列出每天有多少个不同的项目。因此，查询结果应该是一个:

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

- Ras

Answer 1

使用group by

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

- gzaxx

Answer 2

下面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);
        }

- Gun