1 public static IEnumerbale<TSouce> Where<TSource>(this IEnumerable<Tsource> source,Func<TSource,bool> predicate);
2 public static IEnumerable<TSource>where<TSource> (this IEnumerable<TSource> source,Func<TSource,int,bool> predicate);

1 var query=db.OrderDetails.Where(o=>o.ID==12345).Select(o=>new{ ProductID=o.ProductID,Qty=o.Qty});

1 List<int> list1=new List<int>(){1,2,3,4,5,6};
2 List<int> list2=new List<int>(){6,4,2,7,9,0};
3  
4 var query=list1.SelectMany(o=>list2);
5 foreach(var q in query)
6      Console.WriteLine("{0}",q);

1 6424790642790642790642790642790642790

 1 List<int> sequence =new List<int>(){1,2,3,4,3,2,4,6,4,2,4};
 2  
 3 var group=sequence.GroupBy(o=>o);
 4 foreach(var g in group)
 5 {
 6      Console.WrilteLine("{0} count:{1}",g.Key,g.Count());
 7 /*计算每个数出现的次数。
 8      GroupBy 设置了使用数列本身值作为Key值，并且利用这个Key 分组产生分组的数据（IGrouping<TKey,TElement类型），再对分组的数据进行汇总。结果如下：
 9  
10 1 count: 1
11 2 count: 3
12 3 count: 2
13 4 count: 4
14 6 count: 1
15 
16 */

 1 var nameValuesGroup=new[]
 2 {
 3      new{name="Allen", value=65,group="A"},
 4      new{name="Abbey",value=120,group="B"},
 5      new{name="Sue",Value=200,group="A"}
 6 };
 7 var lookupValues=namValuesGroup.ToLookup(c=>c.group);
 8 foreach(var g in lookupValues)
 9 {
10      Console.WriteLine("===Group: {0}===",g.Key);
11      foreach(var item in g)
12      {
13           Console.WriteLine("name:{0},value:{1}",item.name,item.value);
14      }
15 }

1 var query=from item1 in list1
2      join item2 in list2 on item1 equals item2
3      select item2;
4 var query3=list1.Join(
5      list2,
6      item1=>item1,
7      item2=>item2,
8      (item1,item2)=>item2
9      );

1 var query4=from item1 in list1
2           join item2 in list2 on item1 equals item2 into g
3           from item in g.DefaultIfEmpty()
4           select new{ v=item1,c=item};
5 var query5=list1.GroupJoin(
6           list2,
7           item1=>item1,
8           item2=>item2,
9           (item1,item2)=>new {v=item1,c=item2.Count()});

 1  var nameValues=new[]
 2 {
 3      new {name="Allen",value=64},
 4      new {name="abbey",value=120},
 5      new {name="slomng",value=330},
 6      new {name="george",value=213}
 7 };
 8 //single sort
 9 var sortedNames=nameValues.OrderBy(c=>c.name);
10 var sortedValues=nameValues.OrderBy(c=>c.value);
11  
12 //multiply sort conditions
13 var sortedByNameValues=nameValues.OrderBy(c=>c.name).ThenBy(c=>c.value);
14 var sortedByValueNames=nameValues.OrderBy(c=>c.value).ThenBy(c=>c.name);

1 var arrayOutput=nameValues.ToArray();
2 var listOutput=nameValues.ToList();
3  
4 var dictOutput1=nameValues.ToDictionary(c=>c.name);
5 var dictOutput2=nameValues.ToDictionary(c=>c.name,c=>value);

 1 public static IEnumberable<TSource> Skip<TSource>(
 2      this IEnumerable<TSource> source,
 3      int count
 4 )
 5 public static IEnumberable<TSource> SkipWhile<TSource>(
 6      this IEnumerable<TSource> source,
 7      Func<TSource,bool> predicate
 8 )
 9 public static IEnumberable<TSource> SkipWhile<TSource>(
10      this IEnumerable<TSource> source,
11      Func<TSource,int ,bool> predicate
12 )
13 public static IEnumberable<TSource> Take<TSource>(
14      this IEnumerable<TSource> source,
15      int count
16 )
17 public static IEnumberable<TSource> TakeWhile<TSource>(
18      this IEnumerable<TSource> source,
19      Func<TSource,bool> predicate
20 )
21 public static IEnumberable<TSource> TakeWhile<TSource>(
22      this IEnumerable<TSource> source,
23      Func<TSource,int ,bool> predicate
24 )

1 var firstLastItems=new []{"zero","two","three","four","five"};
2 string firstContainsO=firstLastItems.First(s=>s.Contains(‘o‘));
3 string lastContainsO=firstLastItems.Last(s=>s.Contains(‘0‘));

1 var firstLastItems=new []{"zero","two","three","four","five"};
2 string itematThree=firstLastITems.ElementAt(2);

 1 double myBalance=100.0;
 2  
 3 int[] withdrawItems={20,10,40,50,10,70,30};
 4  
 5 double balance=withdrawItems.Aggregate(myBalance,(originbalance,nextWithdrawal)=>{
 6      Console.WriteLine("originbalance:{0},nextWithdrawak:{1}",originbalance,nextdrawal);
 7      Console.WriteLine("Withdrawal status:{0}",(nextWithdrawal<=originbalance)>"OK":"FAILED");
 8  
 9      return ((nextWithdrawal<=originbalance)?(originbalance-nextWithdrawal):originbalance);
10 });
11 Console.WriteLine("Ending balance:{0}:",balance);

1 var balanceStatus=
2 withdrawItems.Aggregate(myBalance,(originbalance,nextWithdrawal)=>{
3      return((nextWithdrawal<=originbalance)?(originbalance-nextWithdrawal):originbalance);
4  
5 },
6 (finalbalance)=>
7 {
8      return (finalbalance>=1000)?"Normal":"Lower";
9 });

1 var racers=from r in Formula1.GetChampions()
2           where r.Wins > 15 && (r.Country=="Brazil"||r.Country=="Austria")
3           select r;
4  
5 foreach(var r in racers)
6 {
7      Console.WriteLine("{0:A}",r);
8 }

1 var racers=Formula1.GetChampions().
2           Where(r=>r.Wins>15 && (r.Country=="Brazil" || r.Country=="Austria")).
3           Select(r=>r);

1 var racers=Formula1.GetChamptions().
2           Where((r,index)=>r.LastName.StartsWith("A") && index % 2 !=0);
3  
4 foreach(var r in racers)
5 {
6      Console.WriteLine("{0,A}",r);
7 }
8      

 1 object[] data={"ones",1,3,"fre","fdfs",333};
 2 var query=data.OfType<string>();
 3 foreach(var s in query)
 4 {
 5      Console.WriteLine(s);
 6 }
 7  /*
 8      运行结果为：
 9  
10 ones
11 fre
12 fdfs
13 */

1 var ferrariDrivers=from r in Formula.GetChampions()
2                     from c in r.Cars
3                     where c=="Ferrari"
4                     orderby r.LastName
5                     select r.FirstName +" "+ r.LastName;

1 public static IEnumerable<TResult> SelectMany<TSource,TCollection,TResult>(this IEnumerable<TSource> source,Func<TSource,IEnumberable<TCollection>> collectionSelector,Func<TSource,TCollection,TResult> resultSelector);

1 var ferrariDrivers= Formula1.GetChampion().
2                     SelectMany(r=>r.Cars,
3                          (r,c)=>new{Racer=r,Car=c}.
4                          where(r=>r.Car=="Ferrari").
5                          OrderBy(r=>r.Racer.LastName).
6                          Select(r=>r.Racer.FirstName+" "+r.Racer.LastName));

1 var racers=from r in Formula1.GetChampions()
2            where r.Country=="Brazil"
3            orderby r.Wins descending
4            select r;

1 var racers= Formula1.GetChampions().
2           Where(r=>r.Country=="Brazil").
3           OrderByDescending(r=>r.Wins).
4           Select(r=>r);

1 var racers=(from r in Formula1.GetChampions()
2                orderby r.Country,r.LastName,r.FirstName
3                select r).Take(10);

1 var racers=Formula1.GetChamptions().
2      OrderBy(r=>r.Country).
3      ThenBy(r=>r.LastName).
4      ThenBy(r=>r.FirstName).
5      Take(10);

 1 var countries= from r in Formula1.GetChampions()
 2                group r by r.Country into g
 3                orderby g.Count() descending, g.Key
 4                where g.Count() >=2
 5                select new {
 6                               Country=g.Key,
 7                               Count=g.Count()
 8                          };
 9 foreach(var item in countries)
10 {
11      Console.WriteLine("{1,-10} {1}",item.Country,item.Count);
12 }

1 var countries= Formula1.GetChampions().
2                GroupBy(r=>r.Country).
3                OrderByDescending(g=>g.Count()).
4                ThenBy(g=>g.Key).
5                Where(g=>g.Count()>=2).
6                Select(g=>new {Country=g.Key,Count=g.Count()});

 1 var countries=from r in Formula1.GetChampions()
 2                group r by r.Country into g
 3                orderby g.Count() descending, g.Key
 4                where g.Count()>=2
 5                select new
 6                {
 7                     Country=g.Key,
 8                     Count=g.Count(),
 9                     Racers=from r1 in g
10                            orderby r1.LastName
11                            select r1.FirstName +" "+ r1.LastName
12                };
13 foreach(var item in countries)
14 {
15      Console.WriteLine("{0,-10} {1}",item.Country,item.Count);
16      foreach(var name in item.Racers)
17      {
18           Console.WriteLine("{0};",name);
19      }
20      Console.WirteLine(); 
21 }

 1 var racers= from r in Formula1.GetChampions()
 2             from y in r.Years
 3             select new
 4             {
 5                Year=y,
 6                Name=r.FirstName+" "+r.LastName
 7              };
 8  
 9 vat teams=from t in Formula1.GetConstructorChampions()
10           from y in t.Years
11           select new
12           {
13                Year=y,
14                Name=t.Name
15           };
16 var racersAndTeams=(from r in racers
17                     join t in teams on r.Year equals t.Year
18                     select new
19                     {
20                          r.Year,
21                          Champion=r.Name,
22                          Constructor=t.Name
23                     }).Take(10);
24 Console.WriteLine("Year World Champion\t Constructor Title");
25 foreach(var item in racersAndTeams)
26 {
27      Console.WriteLine("{0}:{1,-20} {2}",item.Year,item.Champion,item.Constructor);
28 }

 1 var racersAndTeams=(from r in
 2                     from r1 in Formula1.GetChampions()
 3                     from yr in r1.Years
 4                     select new
 5                     {
 6                          Year=yr,
 7                          Name=r1.FirstName+" "+r1.LastName
 8                     }
 9                     join t in
10                          from t1 in Formula1.GetConstructorChampions()
11                          from yt in t1.Years
12                          select new
13                          {
14                               Year=yt,
15                               Name=t1.Name
16                          }
17                     on r.Year equals t.Year
18                     orderby t.Year
19                     select new
20                     {
21                          Year=r.Year,
22                          Racer=r.Name,
23                          Team=t.Name
24                     }).Take(10);

 1 var racersAndTeams=
 2      (from r in racers
 3      join t in teams on r.Year equals t.Year into rt
 4      from t in rt.DefaultIfEmpty()
 5      orderby r.Year
 6      select new
 7      {
 8           Year=r.Year,
 9           Champion=r.Name,
10           Constructor=t==null?"no constructor championship":t.Name
11      }).Take(10);

1 public class Championship
2 {
3      public int Year{get;set;}
4      public string First{get;set;}
5      public string Second{get;set;}
6      public string Third{get;set;}
7 }

 1 private static List<Championship> championships;
 2 public static IEnumerable<Championship> GetChampionships()
 3 {
 4      if(championships == null)
 5      {
 6           championships=new List<Championship>();
 7           championships.Add(new Championship
 8           {
 9                Year=1950,
10                First="Nino Farina",
11                Second="Juan Manuel Fangio",
12                Third="Luigi Fagioli"
13           });
14           championships.Add(new Championship
15           {
16                Year=1951,
17                First="Juan Manuel Fangio",
18                Second="Alberto Ascari",
19                Third="Froliab Gonzalez"
20           });
21      }

1 public class RacerInfo
2 {
3      public int Year{get;set;}
4      public int Position {get;set;}
5      public string FirstName{get;set;}
6      public string LastName{get;set;}
7 }

 1 var racers=Formula1.GetChampionships()
 2           .SelectMany(cs=>new List<RacerInfo>()
 3           {
 4                new RacerInfo{
 5                     Year=cs.Year,
 6                     Position=1,
 7                     FirstName=cs.First.FirstName(),
 8                     LastName=cs.Last.LastName()
 9                },
10                new RacerInfo{
11                     Year=cs.Year,
12                     Position=2,
13                     FirstName=cs.Fisrt.FirstName(),
14                     LastName=cs.Last.LastName()
15                },
16                new RacerInfo{
17                     Year=cs.Year,
18                     Position=3,
19                     FirstName=cs.First.FirstName(),
20                     LastName=cs.Last.LastName()
21                }
22           });

 1 public static class StringExtension
 2 {
 3      public static string FirstName(this string name)
 4      {
 5           int ix=name.LastIndexOf(‘ ‘);
 6           return name.Substring(0,ix);
 7      }
 8      public static string LastName(this string name)
 9      {
10           int ix=name.LastIndexOf(‘ ‘);
11           return name.Substring(ix+1);
12      }
13 }

 1 var q=(from r in Formula1.GetChampions()
 2           join r2 in racers on
 3           new
 4           {
 5                FirstName=r.FirstName,
 6                LastName=r.LastName
 7           }
 8           equals
 9           new
10           {
11                FisrtName=r2.FirstName,
12                LastName=r2.LastName
13           }
14           into yearResults
15           select new
16           {
17                FirstName=r.FirstName,
18                LastName=r.LastName,
19                Wins=r.Wins,
20                Stars=r.Stars,
21                Results=yearResults
22           });
23 foreach(var r in q)
24 {
25      Console.WriteLine("{0} {1}",r.FirstName,r.LastName);
26      foreach(var results in r.Results)
27      {
28           Console.WriteLine("{0} {1}.",results.Year,results.Position);
29      }
30 }

1 var ferrariDrivers=from r in
2                     Formula1.GetChampions()
3                     from c in r.Cars
4                     where c =="Ferrari"
5                     orderby r.LastName
6                     select r;

1 private static IEnumerable<Racer> GetRacersByCar(string car)
2 {
3      return from r in Formula1.GetChampions()
4                from c in r.Cars
5                where c==car 
6                orderby r.LastName
7                select r;
8 }

1 Func<string , IEnumerable<Racer>> racersByCar=
2                car=>from r in Formula1.GetChampions()
3                     from c in r.Cars
4                     where c==car
5                     orderby r.LastName
6                     select r;

1 Console.WriteLine("World champion with Ferrari and McLaren");
2 foreach(var racer in racersByCar("Ferraris").Interesect(racersByCar("McLaren")))
3 {
4      Console.WirteLine(racer);
5 }

 1 var racerNames=from r in Formula1.GetChampions()
 2                where r.Country =="Italy"
 3                orderby r.Wins descending
 4                select new
 5                {
 6                     Name=r.FirstName +" "+ r.LastName
 7                };
 8 var racerNamesAndStarts=from r in Formula1.GetChampions()
 9                          where r.Country="Italy"
10                          orderby r.Wins descending
11                          select new
12                          {
13                               LastName=r.LastName,
14                               Starts=r.Starts
15                          };
16 var racers=racerNames.Zip(racerNamesAndStarts,(first,second)=>first.Name+", starts: "+second.Starts);
17 foreach(var r in racers)
18 {
19      Console.WriteLine(r);
20 }

 1 int pageSize=5;
 2  
 3 int numberPages=(int)Math.Ceiling(Formula1.GetChampions().Count()/(double)pageSize);
 4 for(int page=0;page<numberPages;page++)
 5 {
 6      Console.WriteLine("Page {0}",page);
 7      var racers=(from r in Formula1.GetChampions()
 8                     orderby r.LastName,r.FirstName
 9                     select r.FirstName+" "+r.LastName).
10                     Skip(page*pageSize).Take(pageSize);
11      foreach(var name in racers)
12      {
13           Console.WriteLine(name);
14       }
15      Console.WriteLine();
16 }
17  

 1 var query=from r in Formula1.GetChampions()
 2           let numberYears=r.Years.Count()
 3           where numberYear>=3
 4           orderby numberYears descending, r.LastName
 5           select new
 6           {
 7                Name=r.FirstName+" "+r.LastName,
 8                TimesChampion=numberYears
 9           };
10 foreach(var r in query)
11 {
12      Console.WriteLine("{0} {1}",r.Name,r.TimesChampion);
13 }     
14  

 1 var countries=(from c in from r in Formula1.GetChampions()
 2                group r by r.Country into c
 3                select new
 4                {
 5                     Country=c.Key,
 6                     Wins=(from r1 in c select r1.Wins).Sum()
 7                }
 8                orderby c.Wins descending, c.Country
 9                select c).Take(5);
10 foreach(var country in countries)
11 {
12      Console.WriteLine("{0} {1}",country.Country,country.Wins);
13 }

1 List<Racer> racers=(from r in Formula1.GetChampions()
2                     where r.Starts>150
3                     orderby r.Starts descending
4                     select r).ToList();
5 foreach(var racer in racers)
6 {
7      Console.WriteLine("{0} {0:S}",racer);
8 }

 1 var racers=(from r in Formula1.GetChampions()
 2                from c in r.Cars
 3                select new
 4                {
 5                     Car=c,
 6                     Racer=r
 7                }).ToLookup(cr=>cr.Car,cr=>cr.Racer);
 8 if(racers.Contains("Williams"))
 9 {
10      foreach(var williamsRacer in Racers["Williams"])
11      {
12           Console.WriteLine(williamsRacer);
13      }
14 }

 1 var list=new System.Collections.ArrayList(Formula1.GetChampions() as System.Collections.ICollection);
 2  
 3 var query= from r in list.Cast<Racer>()
 4           where r.Country=="USA"
 5           orderby r.Wins descending
 6           select r;
 7 foreach(var racer in query)
 8 {
 9      Console.WriteLine("{0:A}",racer);
10 }

1 var values =Enumerable.Range(1,20);
2 foreach(var item in values)
3 {
4      Console.WriteLine("{0}",item);
5 }
6 Console.WriteLine();
7  
8 //结果 1 2 3 4 5 6 ......  19 20

1 var values =Enumerable.Range(1,20).Select(n=>n*3);