101个Linq例子(40-60)

GroupBy - Simple 2

 public void Linq41() 
    { 
        string[] words = { "blueberry", "chimpanzee", "abacus", "banana", "apple", "cheese" }; 
      
        var wordGroups = 
            from w in words 
            group w by w[0] into g 
            select new { FirstLetter = g.Key, Words = g }; 
      
        foreach (var g in wordGroups) 
        { 
            Console.WriteLine("Words that start with the letter '{0}':", g.FirstLetter); 
            foreach (var w in g.Words) 
            { 
                Console.WriteLine(w); 
            } 
        } 
    } 

Result

Words that start with the letter 'b':
blueberry
banana
Words that start with the letter 'c':
chimpanzee
cheese
Words that start with the letter 'a':
abacus
apple

GroupBy - Simple 3

 public void Linq42() 
    { 
        List<Product> products = GetProductList(); 
      
        var orderGroups = 
            from p in products 
            group p by p.Category into g 
            select new { Category = g.Key, Products = g }; 
      
        ObjectDumper.Write(orderGroups, 1); 
    } 

 Result

Category=Beverages Products=...
Products: ProductID=1 ProductName=Chai Category=Beverages UnitPrice=18.0000 UnitsInStock=39
Products: ProductID=2 ProductName=Chang Category=Beverages UnitPrice=19.0000 UnitsInStock=17
Products: ProductID=24 ProductName=Guaraná Fantástica Category=Beverages UnitPrice=4.5000 UnitsInStock=20
Products: ProductID=34 ProductName=Sasquatch Ale Category=Beverages UnitPrice=14.0000 UnitsInStock=111
Products: ProductID=35 ProductName=Steeleye Stout Category=Beverages UnitPrice=18.0000 UnitsInStock=20
Products: ProductID=38 ProductName=Côte de Blaye Category=Beverages UnitPrice=263.5000 UnitsInStock=17
Products: ProductID=39 ProductName=Chartreuse verte Category=Beverages UnitPrice=18.0000 UnitsInStock=69
Products: ProductID=43 ProductName=Ipoh Coffee Category=Beverages UnitPrice=46.0000 UnitsInStock=17
Products: ProductID=67 ProductName=Laughing Lumberjack Lager Category=Beverages UnitPrice=14.0000 UnitsInStock=52
Products: ProductID=70 ProductName=Outback Lager Category=Beverages UnitPrice=15.0000 UnitsInStock=15
Products: ProductID=75 ProductName=Rhönbräu Klosterbier Category=Beverages UnitPrice=7.7500 UnitsInStock=125
Products: ProductID=76 ProductName=Lakkalikööri Category=Beverages UnitPrice=18.0000 UnitsInStock=57
Category=Condiments Products=...
Products: ProductID=3 ProductName=Aniseed Syrup Category=Condiments UnitPrice=10.0000 UnitsInStock=13
Products: ProductID=4 ProductName=Chef Anton's Cajun Seasoning Category=Condiments UnitPrice=22.0000 UnitsInStock=53

GroupBy - Nested

   public void Linq43() 
    { 
        List<Customer> customers = GetCustomerList(); 
      
        var customerOrderGroups = 
            from c in customers 
            select 
                new 
                { 
                    c.CompanyName, 
                    YearGroups = 
                        from o in c.Orders 
                        group o by o.OrderDate.Year into yg 
                        select 
                            new 
                            { 
                                Year = yg.Key, 
                                MonthGroups = 
                                    from o in yg 
                                    group o by o.OrderDate.Month into mg 
                                    select new { Month = mg.Key, Orders = mg } 
                            } 
                }; 
      
        ObjectDumper.Write(customerOrderGroups, 3); 
    } 
 

Result

CompanyName=Alfreds Futterkiste YearGroups=...
YearGroups: Year=1997 MonthGroups=...
MonthGroups: Month=8 Orders=...
Orders: OrderID=10643 OrderDate=8/25/1997 Total=814.50
MonthGroups: Month=10 Orders=...
Orders: OrderID=10692 OrderDate=10/3/1997 Total=878.00
Orders: OrderID=10702 OrderDate=10/13/1997 Total=330.00
YearGroups: Year=1998 MonthGroups=...
MonthGroups: Month=1 Orders=...
Orders: OrderID=10835 OrderDate=1/15/1998 Total=845.80
MonthGroups: Month=3 Orders=...
Orders: OrderID=10952 OrderDate=3/16/1998 Total=471.20
MonthGroups: Month=4 Orders=...
Orders: OrderID=11011 OrderDate=4/9/1998 Total=933.50
CompanyName=Ana Trujillo Emparedados y helados YearGroups=...
YearGroups: Year=1996 MonthGroups=...
MonthGroups: Month=9 Orders=...
Orders: OrderID=10308 OrderDate=9/18/1996 Total=88.80
YearGroups: Year=1997 MonthGroups=...
MonthGroups: Month=8 Orders=...
Orders: OrderID=10625 OrderDate=8/8/1997 Total=479.75
MonthGroups: Month=11 Orders=...
Orders: OrderID=10759 OrderDate=11/28/1997 Total=320.00
YearGroups: Year=1998 MonthGroups=...
MonthGroups: Month=3 Orders=...

GroupBy - Comparer

 public void Linq44() 
    { 
        string[] anagrams = { "from   ", " salt", " earn ", "  last   ", " near ", " form  " }; 
      
        var orderGroups = anagrams.GroupBy(w => w.Trim(), new AnagramEqualityComparer()); 
      
        ObjectDumper.Write(orderGroups, 1); 
    } 
      
    public class AnagramEqualityComparer : IEqualityComparer<string> 
    { 
        public bool Equals(string x, string y) 
        { 
            return getCanonicalString(x) == getCanonicalString(y); 
        } 
      
        public int GetHashCode(string obj) 
        { 
            return getCanonicalString(obj).GetHashCode(); 
        } 
      
        private string getCanonicalString(string word) 
        { 
            char[] wordChars = word.ToCharArray(); 
            Array.Sort<char>(wordChars); 
            return new string(wordChars); 
        } 
    } 

Result

...
from 
form 
...
salt
last 
...
earn 
near

GroupBy - Comparer, Mapped

  public void Linq45() 
    { 
        string[] anagrams = { "from   ", " salt", " earn ", "  last   ", " near ", " form  " }; 
      
        var orderGroups = anagrams.GroupBy( 
                    w => w.Trim(), 
                    a => a.ToUpper(), 
                    new AnagramEqualityComparer() 
                    ); 
      
        ObjectDumper.Write(orderGroups, 1); 
    } 
      
    public class AnagramEqualityComparer : IEqualityComparer<string> 
    { 
        public bool Equals(string x, string y) 
        { 
            return getCanonicalString(x) == getCanonicalString(y); 
        } 
      
        public int GetHashCode(string obj) 
        { 
            return getCanonicalString(obj).GetHashCode(); 
        } 
      
        private string getCanonicalString(string word) 
        { 
            char[] wordChars = word.ToCharArray(); 
            Array.Sort<char>(wordChars); 
            return new string(wordChars); 
        } 
    } 

 Result

...
FROM 
FORM 
...
SALT
LAST 
...
EARN 
NEAR

Distinct - 1

public void Linq46() 
{ 
    int[] factorsOf300 = { 2, 2, 3, 5, 5 }; 
  
    var uniqueFactors = factorsOf300.Distinct(); 
  
    Console.WriteLine("Prime factors of 300:"); 
    foreach (var f in uniqueFactors) 
    { 
        Console.WriteLine(f); 
    } 
}

Result

Prime factors of 300:
2
3
5

Distinct - 2

public void Linq47() 
{ 
    List<Product> products = GetProductList(); 
  
    var categoryNames = ( 
        from p in products 
        select p.Category) 
        .Distinct(); 
  
    Console.WriteLine("Category names:"); 
    foreach (var n in categoryNames) 
    { 
        Console.WriteLine(n); 
    } 
}

 Result

Category names:
Beverages
Condiments
Produce
Meat/Poultry
Seafood
Dairy Products
Confections
Grains/Cereals

Union - 1

public void Linq48() 
{ 
    int[] numbersA = { 0, 2, 4, 5, 6, 8, 9 }; 
    int[] numbersB = { 1, 3, 5, 7, 8 }; 
  
    var uniqueNumbers = numbersA.Union(numbersB); 
  
    Console.WriteLine("Unique numbers from both arrays:"); 
    foreach (var n in uniqueNumbers) 
    { 
        Console.WriteLine(n); 
    } 
}

Result

Unique numbers from both arrays:
0
2
4
5
6
8
9
1
3
7

Union - 2

public void Linq49() 
{ 
    List<Product> products = GetProductList(); 
    List<Customer> customers = GetCustomerList(); 
  
    var productFirstChars = 
        from p in products 
        select p.ProductName[0]; 
    var customerFirstChars = 
        from c in customers 
        select c.CompanyName[0]; 
  
    var uniqueFirstChars = productFirstChars.Union(customerFirstChars); 
  
    Console.WriteLine("Unique first letters from Product names and Customer names:"); 
    foreach (var ch in uniqueFirstChars) 
    { 
        Console.WriteLine(ch); 
    } 
}

Result

Unique first letters from Product names and Customer names:
C
A
G
U
N
M
I
Q
K
T
P
S
R
B
J
Z
V
F
E
W
L
O
D
H

Intersect - 1

public void Linq50() 
{ 
    int[] numbersA = { 0, 2, 4, 5, 6, 8, 9 }; 
    int[] numbersB = { 1, 3, 5, 7, 8 }; 
  
    var commonNumbers = numbersA.Intersect(numbersB); 
  
    Console.WriteLine("Common numbers shared by both arrays:"); 
    foreach (var n in commonNumbers) 
    { 
        Console.WriteLine(n); 
    } 
}

 Result

 

Common numbers shared by both arrays:
5
8

Intersect - 2

public void Linq51() 
{ 
    List<Product> products = GetProductList(); 
    List<Customer> customers = GetCustomerList(); 
  
    var productFirstChars = 
        from p in products 
        select p.ProductName[0]; 
    var customerFirstChars = 
        from c in customers 
        select c.CompanyName[0]; 
  
    var commonFirstChars = productFirstChars.Intersect(customerFirstChars); 
  
    Console.WriteLine("Common first letters from Product names and Customer names:"); 
    foreach (var ch in commonFirstChars) 
    { 
        Console.WriteLine(ch); 
    } 
}

Result

 

Common first letters from Product names and Customer names:
C
A
G
N
M
I
Q
K
T
P
S
R
B
V
F
E
W
L
O

Except - 1

 

public void Linq52() 
{ 
    int[] numbersA = { 0, 2, 4, 5, 6, 8, 9 }; 
    int[] numbersB = { 1, 3, 5, 7, 8 }; 
  
    IEnumerable<int> aOnlyNumbers = numbersA.Except(numbersB); 
  
    Console.WriteLine("Numbers in first array but not second array:"); 
    foreach (var n in aOnlyNumbers) 
    { 
        Console.WriteLine(n); 
    } 
}

 Result

Numbers in first array but not second array:
0
2
4
6
9

Except - 2

public void Linq53() 
{ 
    List<Product> products = GetProductList(); 
    List<Customer> customers = GetCustomerList(); 
  
    var productFirstChars = 
        from p in products 
        select p.ProductName[0]; 
    var customerFirstChars = 
        from c in customers 
        select c.CompanyName[0]; 
  
    var productOnlyFirstChars = productFirstChars.Except(customerFirstChars); 
  
    Console.WriteLine("First letters from Product names, but not from Customer names:"); 
    foreach (var ch in productOnlyFirstChars) 
    { 
        Console.WriteLine(ch); 
    } 
}

Result

First letters from Product names, but not from Customer names:
U
J
Z

 

ToArray

public void Linq54() 
{ 
    double[] doubles = { 1.7, 2.3, 1.9, 4.1, 2.9 }; 
  
    var sortedDoubles = 
        from d in doubles 
        orderby d descending 
        select d; 
    var doublesArray = sortedDoubles.ToArray(); 
  
    Console.WriteLine("Every other double from highest to lowest:"); 
    for (int d = 0; d < doublesArray.Length; d += 2) 
    { 
        Console.WriteLine(doublesArray[d]); 
    } 
}

Result

Every other double from highest to lowest:
4.1
2.3
1.7

ToList

public void Linq55() 
{ 
    string[] words = { "cherry", "apple", "blueberry" }; 
  
    var sortedWords = 
        from w in words 
        orderby w 
        select w; 
    var wordList = sortedWords.ToList(); 
  
    Console.WriteLine("The sorted word list:"); 
    foreach (var w in wordList) 
    { 
        Console.WriteLine(w); 
    } 
}

Result

The sorted word list:
apple
blueberry
cherry

ToDictionary

public void Linq56() 
{ 
    var scoreRecords = new[] { new {Name = "Alice", Score = 50}, 
                                new {Name = "Bob"  , Score = 40}, 
                                new {Name = "Cathy", Score = 45} 
                            }; 
  
    var scoreRecordsDict = scoreRecords.ToDictionary(sr => sr.Name); 
  
    Console.WriteLine("Bob's score: {0}", scoreRecordsDict["Bob"]); 
}

Result

Bob's score: { Name = Bob, Score = 40 }

OfType

public void Linq57() 
{ 
    object[] numbers = { null, 1.0, "two", 3, "four", 5, "six", 7.0 }; 
  
    var doubles = numbers.OfType<double>(); 
  
    Console.WriteLine("Numbers stored as doubles:"); 
    foreach (var d in doubles) 
    { 
        Console.WriteLine(d); 
    } 
}

Result

Numbers stored as doubles:
1
7

First - Simple

public void Linq58() 
{ 
    List<Product> products = GetProductList(); 
 
    Product product12 = ( 
        from p in products 
        where p.ProductID == 12 
        select p) 
        .First(); 
  
    ObjectDumper.Write(product12); 
}

Result

ProductID=12 ProductName=Queso Manchego La Pastora Category=Dairy Products UnitPrice=38.0000 UnitsInStock=86

First - Condition

public void Linq59() 
{ 
    string[] strings = { "zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine" }; 
  
    string startsWithO = strings.First(s => s[0] == 'o'); 
  
    Console.WriteLine("A string starting with 'o': {0}", startsWithO); 
}

Result

A string starting with 'o': one

FirstOrDefault - Simple

public void Linq61() 
  
{ 
    int[] numbers = { }; 
  
    int firstNumOrDefault = numbers.FirstOrDefault(); 
  
    Console.WriteLine(firstNumOrDefault); 
}

Result

0