Linq--标准的查询操作符
===========================================Racer.cs
专注于为中小企业提供成都做网站、网站设计服务,电脑端+手机端+微信端的三站合一,更高效的管理,为中小企业京山免费做网站提供优质的服务。我们立足成都，凝聚了一批互联网行业人才，有力地推动了成百上千家企业的稳健成长，帮助中小企业通过网站建设实现规模扩充和转变。
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Collections;
namespace ConsoleApplication4
{
[Serializable]
public class Racer:IComparable,IFormattable
{
public string FirstName { get; private set; }//第一个武将
public string LastName { get; private set; }//第二个武将
public int Wins { get; private set; }//赢得次数
public string Country { get; private set; }//国家
public int Starts { get; private set; }//开始
public string[] Arms { get; private set; }//武器
public int[] Years { get; private set; }//年份
public Racer(string firstname = "", string lasename = "", int wins = 0, string country = "", int starts = 0, IEnumerable Arms = null, IEnumerable years = null)
{
this.FirstName = firstname;
this.LastName = lasename;
this.Wins = wins;
this.Country = country;
this.Starts = starts;
List LArms = new List();
foreach (var item in Arms)
{
LArms.Add(item);
}
this.Arms = LArms.ToArray();
List Lyears = new List();
foreach (var item in years)
{
Lyears.Add(item);
}
this.Years = Lyears.ToArray();
}
public int CompareTo(Racer other)
{
if (other == null) throw new ArgumentNullException("对象不能为空");
return this.Wins.CompareTo(other.Wins);
}
public string ToString(string format, IFormatProvider formatProvider)
{
switch (format)
{
case "":
return ToString();
case "C":
StringBuilder sb = new StringBuilder();
foreach (var item in Arms)
{
sb.Append(item + ",");
}
return sb.ToString().TrimEnd(',');
case "Y":
StringBuilder sb2 = new StringBuilder();
foreach (var item in Years)
{
sb2.Append(item + ",");
}
return sb2.ToString().TrimEnd(',');
default:
return ToString();
}
}
public override string ToString()
{
return string.Format("第一个赛手：{0},最后一个赛手：{1},赢的次数：{2},国家：{3},开始：{4}",this.FirstName,this.LastName,this.Wins.ToString(),this.Country,this.Starts.ToString());
}
}
} ===========================================Team.cs
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace ConsoleApplication4
{
[Serializable]
public class Team
{
public string Name { get; private set; }//团队名称
public int[] Years { get; private set; }
public Team(string name,params int[] years)
{
this.Name = name;
this.Years = years;
}
}
}===========================================Formula.cs
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace ConsoleApplication4
{
public static class Formula
{
private static List racers;
private static List team;
public static IList GetChampions()
{
if (racers == null)
{
racers = new List();
racers.Add(new Racer("张飞", "关羽", 100, "蜀国", 10, new string[] { "丈八蛇矛", "青龙偃月刀" }, new int[] { 200, 201, 202 }));
racers.Add(new Racer("张飞", "关羽", 99, "蜀国", 10, new string[] { "丈八蛇矛", "青龙偃月刀" }, new int[] { 200, 201, 202 }));
racers.Add(new Racer("黄忠", "魏延", 80, "蜀国", 10, new string[] { "穿杨弓", "大***" }, new int[] {203}));
racers.Add(new Racer("许褚", "典韦", 95, "魏国", 10, new string[] { "大铁锤", "双戟" }, new int[] { 195, 212 }));
racers.Add(new Racer("张辽", "徐晃", 90, "魏国", 10, new string[] { "长把子刀", "长把子斧" }, new int[] { 205, 106, 215 }));
racers.Add(new Racer("程普", "黄盖", 96, "吴国", 10, new string[] { "龙虎鞭", "大刀" }, new int[] { 190, 191, 202,207 }));
racers.Add(new Racer("周泰", "太史慈", 88, "吴国", 10, new string[] { "无敌身躯", "火箭枪" }, new int[] { 195, 196, 197 }));
}
return racers;
}
public static IList GetConstructorChampions()
{
if (team == null)
{
team = new List();
team.Add(new Team("兄弟队", new int[] { 200, 201, 202 }));
team.Add(new Team("死党队", new int[] { 203 }));
team.Add(new Team("虎营队", new int[] { 195, 212 }));
team.Add(new Team("良将队", new int[] { 205, 106, 215 }));
team.Add(new Team("老将队", new int[] { 190, 191, 202, 207 }));
team.Add(new Team("不死队", new int[] { 195, 196, 197 }));
}
return team;
}
}
} ===========================================Racer_IEqualityComparer.cs
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace ConsoleApplication4
{
public class Racer_IEqualityComparer:IEqualityComparer
{
//只比较Racer对象的FirstName属性
public bool Equals(Racer x, Racer y)
{
return x.FirstName==y.FirstName;
}
public int GetHashCode(Racer obj)
{
return obj.FirstName.GetHashCode();
}
}
} ===========================================主程序
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Collections;
using System.Collections.Concurrent;
namespace ConsoleApplication4
{
class Program
{
static void Main(string[] args)
{
//筛选(查询赢了至少95场的吴国和蜀国军队军队)***************************************************************
//--Linq
var query1 = from r in Formula.GetChampions()
where r.Wins >= 95 && (r.Country == "吴国" || r.Country == "蜀国")
select r;
//--扩展方法
IEnumerable ir1 = Formula.GetChampions().
Where(r => r.Wins >= 95 && (r.Country == "吴国" || r.Country == "蜀国")).Select(r => r);
Foreach(query1);
Foreach(ir1);
//索引筛选(查询赢了大于85场的、索引为偶数的军团)************************************************************
//--扩展方法
IEnumerable ir2 = Formula.GetChampions().Where((r, index) => r.Wins > 85 && index % 2 == 0).Select(r => r);
Foreach(Formula.GetChampions());
Foreach(ir2);
//类型筛选**************************************************************************************************
//--扩展方法
object[] o = new object[] { 1, 2, "张飞", 2, "关二爷", true, 1.1 };
IEnumerable is1 = o.OfType();//筛选为string类型的元素
Foreach(is1);
//复合from子句(查询所有的武器)*******************************************************************************
//--Linq
var query2 = from r in Formula.GetChampions()
from c in r.Arms
select c;
Foreach(query2);
//--扩展方法
IEnumerable is2 = Formula.GetChampions().SelectMany(r => r.Arms, (r, a) => new { Racer = r, Amrs = a }).
Select(r => r.Racer.FirstName + "|" + r.Racer.LastName + "=>" + r.Amrs);
Foreach(is2);
//排序(先按照第一个姓名降序排序，在按照赢得次数升序排序,返回10个数据)****************************************
//--Linq
var query3 = (from r in Formula.GetChampions()
orderby r.FirstName descending, r.Wins ascending
select r).Take(10);
Foreach(query3);
//--扩展方法
IEnumerable is3 = Formula.GetChampions().OrderByDescending(r => r.FirstName).ThenBy(r => r.Wins).Select(r => r);//第一种方法（ThenBy）
IEnumerable is4 = Formula.GetChampions().OrderByDescending(r => r.FirstName).
CreateOrderedEnumerable(r => r.Wins, Comparer.Default, true).Select(r => r).Take(10);//第二种方法（CreateOrderedEnumerable）
Foreach(is4);
//分组(根据国家分组，并且只显示军团大于或等于2的国家)************************************************************
//--Linq
var query4 = from r in Formula.GetChampions()
group r by r.Country into g
where g.Count() >= 2
select new
{
Count = g.Count(),
Key = g.Key
};
foreach (var item in query4)
{
Console.WriteLine("国家：{0}。军团数：{1}", item.Key, item.Count);
}
//--扩展方法
var is5 = Formula.GetChampions().GroupBy(r => r.Country).Where(r => r.Count() >= 2).Select(r => new { Count = r.Count(), Key = r.Key });
foreach (var item in is5)
{
Console.WriteLine("国家：{0}。军团数：{1}", item.Key, item.Count);
}
Console.WriteLine("================================================");
//对嵌套的对象分组(对国家进行分组，查询出国家名称，国家的军团数，军队的将军)******************************
//--Linq
var query5 = from r in Formula.GetChampions()
group r by r.Country into g
select new
{
Key = g.Key,
Count = g.Count(),
Name = from n in g
select new
{
LastName = n.LastName,
FirstName = n.FirstName
}
};
foreach (var item in query5)
{
Console.WriteLine("国家：{0}。军团数：{1}", item.Key, item.Count);
foreach (var subitem in item.Name)
{
Console.WriteLine("军队的将军：" + subitem.FirstName + "|" + subitem.LastName);
}
}
Console.WriteLine("================================================");
//--扩展方法
var is6 = Formula.GetChampions().GroupBy(r => r.Country).
Select(r => new { Country = r.Key, Count = r.Count(), Name = r.Select(n => new { FristName = n.FirstName, LastName = n.LastName }) });
foreach (var item in query5)
{
Console.WriteLine("国家：{0}。军团数：{1}", item.Key, item.Count);
foreach (var subitem in item.Name)
{
Console.WriteLine("军队的将军：" + subitem.FirstName + "|" + subitem.LastName);
}
}
Console.WriteLine("================================================");
//连接（查询年份大于195的军团和将军）******************************************************************************
//--Linq 【语法： from r in 第一个对象 join t in 第二个对象 on r.one equals t.one select new { }】
int myyear = 190;
var query7 = from racer in
from r in Formula.GetChampions()
from ry in r.Years
where ry > myyear
select new
{
Year = ry,
Name = r.FirstName + "|" + r.LastName
}
join team in
from t in Formula.GetConstructorChampions()
from ty in t.Years
where ty > myyear
select new
{
Year = ty,
Name = t.Name
}
on racer.Year equals team.Year
select new
{
TeamName = team.Name,
Year = team.Year,
Name = racer.Name
};
foreach (var item in query7)
{
Console.WriteLine("军团：{0},将军：{1}，年份：{2}", item.TeamName, item.Name, item.Year);
}
Console.WriteLine("================================================");
//集合操作**********************************************************************************************************************
//Racer_IEqualityComparer类实现了IEqualityComparer,只比较Racer对象的FirstName属性
//委托，传一个武器名称，查询属于该武器的所有元素
Func> myracer = racer => from r in Formula.GetChampions()
from a in r.Arms
where a == racer
select r;
//----Distinct() 排除重复的数据
Foreach(Formula.GetChampions().Distinct(new Racer_IEqualityComparer()));
//----Union() 并集 【(1,2,3,5)并集(5,6)=(1,2,3,5,6)】
Foreach(myracer("长把子刀").Union(myracer("大***")));
//----Intersect 交集 【(1,2,3,5)交集(5,6)=(5)】
Foreach(Formula.GetChampions().Intersect(myracer("大***")));
//----Except 差集 【(1,2,3,5)差集(5,6)=(1,2,3)】
Foreach(Formula.GetChampions().Except(myracer("大***")));
//合并*************************************************************************************************************************
Foreach(myracer("长把子刀").Zip(myracer("大***"), (r, t) => r.FirstName + "|" + t.FirstName));//输出：张辽|黄忠
//分区【Skip：跳过指定数量的元素】【Take：显示的数量】*************************************************************************
int pageindex = 1;//当前页
int pagesize = 3;//每夜显示多少数据
Foreach(Formula.GetChampions().Skip(pageindex * pagesize).Take(pagesize));
//聚合操作符（返回一个值）******************************************************************************************************
//----Count() 返回集合中的项数
Foreach(from r in Formula.GetChampions() select r.Years.Count());
//----Sum() 返回所有数字的和
Console.WriteLine((from r in Formula.GetChampions() select r.Years.Count()).Sum());
//----Min() 返回集合中最小的元素
Console.WriteLine((from r in Formula.GetChampions() select r.Years.Count()).Min());
//----Max() 返回集合中最小的元素
Console.WriteLine((from r in Formula.GetChampions() select r.Years.Count()).Max());
//----Average() 返回集合的平均值
Console.WriteLine((from r in Formula.GetChampions() select r.Years.Count()).Average());
//----Aggregate() 聚合运算
Console.WriteLine((from r in Formula.GetChampions() select r.Years.Count()).Aggregate((a, b) => a * b));
//转换（根据将军查询武器）***********************************************************************************************
//查询可以推迟到访问数据项时再执行，在迭代中使用查询时，查询会执行。而使用转换操作符会立即执行查询，把查询放在数组，列表或字典中
var query8 = (from r in Formula.GetChampions()
select new
{
Name = r.FirstName,
Racer = r
}).ToList().ToLookup(r => r.Name, r => r.Racer);
Foreach(query8["张飞"]);
//在非类型化的集合上（如ArrayList）使用Linq查询，就可以使用cast()方法
ArrayList abc= new ArrayList();
var aaaaa = (from ii in abc.Cast() select ii);
//操作符*****************************************************************************************************************
//--填充一个范围的数字
Foreach(Enumerable.Range(1, 20).Where(r => r > 10).Select(r => r));
//--返回一个空集合
List l = Enumerable.Empty().ToList();
//生成一个重复值的序列
Foreach(Enumerable.Repeat("asd", 3));
Console.ReadKey();
}
static void Foreach(IEnumerable s)
{
foreach (T item in s)
{
Console.WriteLine(item);
}
//Parallel.ForEach(s, i => Console.WriteLine(i));
Console.WriteLine("=========================");
}
}
} 
文章标题：Linq--标准的查询操作符
文章网址：http://ybzwz.com/article/jdpids.html
