LINQ - 使用类型计数对对象进行分组

Question

我有一个对象集合，每个对象都由特定的“组”定义。如何编写 LINQ 查询来生成按“组”分组的每个对象的计数。

举个例子，假设我有以下课程；

public class Release 
{
     int ReleaseNumber; 

     public ReleaseDetails[] details;

}

public class ReleaseDetails
{
    string Group;

    // other details omitted
}

对于给定的版本，我希望能够产生如下输出：

Release number 1 contains the following details;
 - 17 records in Group A
 - 12 records in Group B
 - 6 records in Group C

非常感谢任何帮助。

Answer 1

您可以执行类似

var q = from d in r.Details
            group d by d.Group into counts
            select new { Count = counts.Count(), Group = counts.Key };

完整示例的操作：

        Release r = new Release
        {
            ReleaseNumber = 1
            ,
            Details = new ReleaseDetails[]
            {
                new ReleaseDetails { Group = "a"},
                new ReleaseDetails { Group = "a"},
                new ReleaseDetails { Group = "b"},
                new ReleaseDetails { Group = "c"},
                new ReleaseDetails { Group = "d"},
                new ReleaseDetails { Group = "d"},
                new ReleaseDetails { Group = "e"},

            }
        };

        var q = from d in r.Details
                group d by d.Group into counts
                select new { Count = counts.Count(), Group = counts.Key };

        foreach (var count in q)
        {
            Console.WriteLine("Group {0}: {1}", count.Group, count.Count);
        }

Answer 2

干得好。

    public class ReleaseDetails
    {
        public string Group { get; set; }
        public ReleaseDetails() {}
        public ReleaseDetails(string grp){Group = grp;}
    }

            var qry = new Release();
            qry.details = new List<ReleaseDetails>();
            qry.details.Add(new ReleaseDetails("A"));
            qry.details.Add(new ReleaseDetails("A"));
            qry.details.Add(new ReleaseDetails("B"));
            qry.details.Add(new ReleaseDetails("C"));
            qry.details.Add(new ReleaseDetails("C"));
            qry.details.Add(new ReleaseDetails("B"));


 var result = from x in qry.details
                group x by x.Group into g
                select new 
                { 
                    Count = g.Count(), 
                    Group = g.Key 
                };

//Or using Labmda
var result1 = qry.details.GroupBy(x => x.Group).Select(g => new { Count = g.Count(), Group = g.Key });