C#3.0新增功能09 LINQ 标准查询运算符 04 运算

string[] words = { "the", "quick", "brown", "fox", "jumps" };  
  
IEnumerable<string> query = from word in words  
                            orderby word.Length  
                            select word;  
  
foreach (string str in query)  
    Console.WriteLine(str);  
  
/* 输出:  
    the  
    fox  
    quick  
    brown  
    jumps  
*/

string[] words = { "the", "quick", "brown", "fox", "jumps" };  
  
IEnumerable<string> query = from word in words  
                            orderby word.Substring(0, 1) descending  
                            select word;  
  
foreach (string str in query)  
    Console.WriteLine(str);  
  
/*  输出：
    the  
    quick  
    jumps  
    fox  
    brown  
*/

string[] words = { "the", "quick", "brown", "fox", "jumps" };  
  
IEnumerable<string> query = from word in words  
                            orderby word.Length, word.Substring(0, 1)  
                            select word;  
  
foreach (string str in query)  
    Console.WriteLine(str);  
  
/* 输出： 
    fox  
    the  
    brown  
    jumps  
    quick  
*/

string[] words = { "the", "quick", "brown", "fox", "jumps" };  
  
IEnumerable<string> query = from word in words  
                            orderby word.Length, word.Substring(0, 1) descending  
                            select word;  
  
foreach (string str in query)  
    Console.WriteLine(str);  
  
/* 输出： 
    the  
    fox  
    quick  
    jumps  
    brown  
*/

string[] words = { "the", "quick", "brown", "fox", "jumps" };  
  
IEnumerable<string> query = from word in words  
                            where word.Length == 3  
                            select word;  
  
foreach (string str in query)  
    Console.WriteLine(str);  
  
/* 输出：
    the  
    fox  
*/

List<string> words = new List<string>() { "an", "apple", "a", "day" };  
  
var query = from word in words  
            select word.Substring(0, 1);  
  
foreach (string s in query)  
    Console.WriteLine(s);  
  
/* 输出：
    a  
    a  
    a  
    d  
*/

List<string> phrases = new List<string>() { "an apple a day", "the quick brown fox" };  
  
var query = from phrase in phrases  
            from word in phrase.Split(' ')  
            select word;  
  
foreach (string s in query)  
    Console.WriteLine(s);  
  
/* 输出：
    an  
    apple  
    a  
    day  
    the  
    quick  
    brown  
    fox  
*/

 1 class Bouquet  
 2 {  
 3     public List<string> Flowers { get; set; }  
 4 }  
 5   
 6 static void SelectVsSelectMany()  
 7 {  
 8     List<Bouquet> bouquets = new List<Bouquet>() {  
 9         new Bouquet { Flowers = new List<string> { "sunflower", "daisy", "daffodil", "larkspur" }},  
10         new Bouquet { Flowers = new List<string> { "tulip", "rose", "orchid" }},  
11         new Bouquet { Flowers = new List<string> { "gladiolis", "lily", "snapdragon", "aster", "protea" }},  
12         new Bouquet { Flowers = new List<string> { "larkspur", "lilac", "iris", "dahlia" }}  
13     };  
14   
15     // *********** Select ***********              
16     IEnumerable<List<string>> query1 = bouquets.Select(bq => bq.Flowers);  
17   
18     // ********* SelectMany *********  
19     IEnumerable<string> query2 = bouquets.SelectMany(bq => bq.Flowers);  
20   
21     Console.WriteLine("Results by using Select():");  
22     // 注意这里额外的foreach循环  
23     foreach (IEnumerable<String> collection in query1)  
24         foreach (string item in collection)  
25             Console.WriteLine(item);  
26   
27     Console.WriteLine("\nResults by using SelectMany():");  
28     foreach (string item in query2)  
29         Console.WriteLine(item);  
30   
31     /* 输出：
32   
33        Results by using Select():  
34         sunflower  
35         daisy  
36         daffodil  
37         larkspur  
38         tulip  
39         rose  
40         orchid  
41         gladiolis  
42         lily  
43         snapdragon  
44         aster  
45         protea  
46         larkspur  
47         lilac  
48         iris  
49         dahlia  
50   
51        Results by using SelectMany():  
52         sunflower  
53         daisy  
54         daffodil  
55         larkspur  
56         tulip  
57         rose  
58         orchid  
59         gladiolis  
60         lily  
61         snapdragon  
62         aster  
63         protea  
64         larkspur  
65         lilac  
66         iris  
67         dahlia  
68     */  
69   
70 }

List<int> numbers = new List<int>() { 35, 44, 200, 84, 3987, 4, 199, 329, 446, 208 };  
  
IEnumerable<IGrouping<int, int>> query = from number in numbers  
                                         group number by number % 2;  
  
foreach (var group in query)  
{  
    Console.WriteLine(group.Key == 0 ? "\nEven numbers:" : "\nOdd numbers:");  
    foreach (int i in group)  
        Console.WriteLine(i);  
}  
  
/*  输出：
    Odd numbers:  
    35  
    3987  
    199  
    329  
  
    Even numbers:  
    44  
    200  
    84  
    4  
    446  
    208  
*/

 1 class Plant  
 2 {  
 3     public string Name { get; set; }  
 4 }  
 5   
 6 class CarnivorousPlant : Plant  
 7 {  
 8     public string TrapType { get; set; }  
 9 }  
10   
11 static void Cast()  
12 {  
13     Plant[] plants = new Plant[] {  
14         new CarnivorousPlant { Name = "Venus Fly Trap", TrapType = "Snap Trap" },  
15         new CarnivorousPlant { Name = "Pitcher Plant", TrapType = "Pitfall Trap" },  
16         new CarnivorousPlant { Name = "Sundew", TrapType = "Flypaper Trap" },  
17         new CarnivorousPlant { Name = "Waterwheel Plant", TrapType = "Snap Trap" }  
18     };  
19   
20     var query = from CarnivorousPlant cPlant in plants  
21                 where cPlant.TrapType == "Snap Trap"  
22                 select cPlant;  
23   
24     foreach (Plant plant in query)  
25         Console.WriteLine(plant.Name);  
26   
27     /* 输出：
28   
29         Venus Fly Trap  
30         Waterwheel Plant  
31     */  
32 }