Demo模型类：
public
class
StudentScore
{
public
int
ID {
set
;
get
; }
public
string
Name {
set
;
get
; }
public
string
Course {
set
;
get
; }
public
int
Score {
set
;
get
; }
public
string
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)
select
new
{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
select
new
{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) >=
80
orderby
grouped.Average(m =>
m.Score) descending
select
new
{
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
