[转]Linq中GroupBy方法的使用总结
内容导读
互联网集市收集整理的这篇技术教程文章主要介绍了[转]Linq中GroupBy方法的使用总结，小编现在分享给大家，供广大互联网技能从业者学习和参考。文章包含5278字，纯文字阅读大概需要8分钟。
内容图文
Demo模型类：
public
class
StudentScore
{
public
int ID { set; get; }
publicstring Name { set; get; }
publicstring Course { set; get; }
publicint Score { set; get; }
publicstring Term { set; get; }
}
Demo示例代码：
static
void
Main()
{
var lst = new List<StudentScore>
{
new StudentScore {ID = 1, Name = "张三", Term = "第一学期", Course = "Math", Score = 80},
new StudentScore {ID = 1, Name = "张三", Term = "第一学期", Course = "Chinese", Score = 90},
new StudentScore {ID = 1, Name = "张三", Term = "第一学期", Course = "English", Score = 70},
new StudentScore {ID = 2, Name = "李四", Term = "第一学期", Course = "Math", Score = 60},
new StudentScore {ID = 2, Name = "李四", Term = "第一学期", Course = "Chinese", Score = 70},
new StudentScore {ID = 2, Name = "李四", Term = "第一学期", Course = "English", Score = 30},
new StudentScore {ID = 3, Name = "王五", Term = "第一学期", Course = "Math", Score = 100},
new StudentScore {ID = 3, Name = "王五", Term = "第一学期", Course = "Chinese", Score = 80},
new StudentScore {ID = 3, Name = "王五", Term = "第一学期", Course = "English", Score = 80},
new StudentScore {ID = 4, Name = "赵六", Term = "第一学期", Course = "Math", Score = 90},
new StudentScore {ID = 4, Name = "赵六", Term = "第一学期", Course = "Chinese", Score = 80},
new StudentScore {ID = 4, Name = "赵六", Term = "第一学期", Course = "English", Score = 70},
new StudentScore {ID = 1, Name = "张三", Term = "第二学期", Course = "Math", Score = 100},
new StudentScore {ID = 1, Name = "张三", Term = "第二学期", Course = "Chinese", Score = 80},
new StudentScore {ID = 1, Name = "张三", Term = "第二学期", Course = "English", Score = 70},
new StudentScore {ID = 2, Name = "李四", Term = "第二学期", Course = "Math", Score = 90},
new StudentScore {ID = 2, Name = "李四", Term = "第二学期", Course = "Chinese", Score = 50},
new StudentScore {ID = 2, Name = "李四", Term = "第二学期", Course = "English", Score = 80},
new StudentScore {ID = 3, Name = "王五", Term = "第二学期", Course = "Math", Score = 90},
new StudentScore {ID = 3, Name = "王五", Term = "第二学期", Course = "Chinese", Score = 70},
new StudentScore {ID = 3, Name = "王五", Term = "第二学期", Course = "English", Score = 80},
new StudentScore {ID = 4, Name = "赵六", Term = "第二学期", Course = "Math", Score = 70},
new StudentScore {ID = 4, Name = "赵六", Term = "第二学期", Course = "Chinese", Score = 60},
new StudentScore {ID = 4, Name = "赵六", Term = "第二学期", Course = "English", Score = 70},
};
//
分组，根据姓名，统计Sum的分数，统计结果放在匿名对象中。两种写法。
//
第一种写法
Console.WriteLine("---------第一种写法");
var studentSumScore_1 = (from l in lst
group l by l.Name
into grouped
orderby grouped.Sum(m => m.Score)
selectnew {Name = grouped.Key, Scores = grouped.Sum(m => m.Score)}).ToList();
foreach (var l in studentSumScore_1)
{
Console.WriteLine("{0}:总分{1}", l.Name, l.Scores);
}
//第二种写法
Console.WriteLine("---------第二种写法");
var studentSumScore_2 = lst.GroupBy(m => m.Name)
.Select(k => new {Name = k.Key, Scores = k.Sum(l => l.Score)})
.OrderBy(m => m.Scores).ToList();
foreach (var l in studentSumScore_2)
{
Console.WriteLine("{0}:总分{1}", l.Name, l.Scores);
}
//分组，根据2个条件学期和课程，统计各科均分,统计结果放在匿名对象中。两种写法。
Console.WriteLine("---------第一种写法");
var TermAvgScore_1 = (from l in lst
group l by new {l.Term, l.Course}
into grouped
orderby grouped.Average(m => m.Score) ascending
orderby grouped.Key.Term descending
selectnew {grouped.Key.Term, grouped.Key.Course, Scores = grouped.Average(m => m.Score)})
.ToList();
foreach (var l in TermAvgScore_1)
{
Console.WriteLine("学期:{0},课程:{1},均分:{2}", l.Term, l.Course, l.Scores);
}
Console.WriteLine("---------第二种写法");
var TermAvgScore_2 = lst.GroupBy(m => new {m.Term, m.Course})
.Select(k => new {k.Key.Term, k.Key.Course, Scores = k.Average(m => m.Score)})
.OrderBy(l => l.Scores).ThenByDescending(l => l.Term);
foreach (var l in TermAvgScore_2)
{
Console.WriteLine("学期:{0},课程:{1},均分:{2}", l.Term, l.Course, l.Scores);
}
//分组，带有Having的查询，查询均分>80的学生
Console.WriteLine("---------第一种写法");
var AvgScoreGreater80_1 = (from l in lst
group l by new {l.Name, l.Term}
into grouped
where grouped.Average(m => m.Score) >= 80orderby grouped.Average(m => m.Score) descending
selectnew
{
grouped.Key.Name,
grouped.Key.Term,
Scores = grouped.Average(m => m.Score)
}).ToList();
foreach (var l in AvgScoreGreater80_1)
{
Console.WriteLine("姓名:{0},学期:{1},均分:{2}", l.Name, l.Term, l.Scores);
}
Console.WriteLine("---------第二种写法");
/*此写法看起来较为复杂，第一个Groupby，由于是要对多个字段分组的，因此构建一个匿名对象，
对这个匿名对象分组，分组得到的其实是一个IEnumberable<IGrouping<匿名类型，StudentScore>>这样一个类型。
Where方法接受，和返回的都同样是IEnumberable<IGrouping<匿名类型，StudentScore>>类型，
其中Where方法签名Func委托的类型也就成了Func<IGrouping<匿名类型，StudentScore>,bool>,
之前说到，IGrouping<out TKey, out TElement>继承了IEnumerable<TElement>,
因此这种类型可以有Average，Sum等方法。 */var AvgScoreGreater80_2 = lst.GroupBy(l => new {l.Name, l.Term})
.Where(m => m.Average(x => x.Score) >= 80)
.OrderByDescending(l => l.Average(x => x.Score))
.Select(l => new {l.Key.Name, l.Key.Term, Scores = l.Average(m => m.Score)}).ToList();
foreach (var l in AvgScoreGreater80_2)
{
Console.WriteLine("姓名:{0},学期:{1},均分:{2}", l.Name, l.Term, l.Scores);
}
Console.ReadKey();
}
原文地址：http://hi.baidu.com/tewuapple/item/5e0e5a2862b67a8b9c63d103
原文：http://www.cnblogs.com/seesky/p/3598502.html
内容总结
以上是互联网集市为您收集整理的[转]Linq中GroupBy方法的使用总结全部内容，希望文章能够帮你解决[转]Linq中GroupBy方法的使用总结所遇到的程序开发问题。 如果觉得互联网集市技术教程内容还不错，欢迎将互联网集市网站推荐给程序员好友。
内容备注
版权声明：本文内容由互联网用户自发贡献，该文观点与技术仅代表作者本人。本站仅提供信息存储空间服务，不拥有所有权，不承担相关法律责任。如发现本站有涉嫌侵权/违法违规的内容， 请发送邮件至 gblab@vip.qq.com 举报，一经查实，本站将立刻删除。
内容手机端
扫描二维码推送至手机访问。
来源：【匿名】