C# LINQ counting elements with DISTINCT

问题

I have a collection of KeyValuePair items with DateTime as key and a string as value. Basically my data looks like:

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

I would like to have a List of how many items (distinct) I've for each days. So the query would result in a:

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

回答1:

use group by

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

回答2:

Below is the solution with complete example

        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);
        }

来源：https://stackoverflow.com/questions/17652301/c-sharp-linq-counting-elements-with-distinct