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[] 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, );
    } 

 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, );
    }
 

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, );
    } 

    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, );
    } 

    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 = { , , , ,  }; 

    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 = { , , , , , ,  };
    int[] numbersB = { , , , ,  }; 

    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[];
    var customerFirstChars =
        from c in customers
        select c.CompanyName[]; 

    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 = { , , , , , ,  };
    int[] numbersB = { , , , ,  }; 

    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[];
    var customerFirstChars =
        from c in customers
        select c.CompanyName[]; 

    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 = { , , , , , ,  };
    int[] numbersB = { , , , ,  }; 

    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[];
    var customerFirstChars =
        from c in customers
        select c.CompanyName[]; 

    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 = ; d < doublesArray.Length; d += )
    {
        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 = },
                                new {Name = "Bob"  , Score = },
                                new {Name = "Cathy", Score = }
                            }; 

    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", , "four", , "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 ==
        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[] == '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