Csharp/C Sharp/LINQ/where

Содержание

1 A Query Using the Standard Dot Notation Syntax
2 Assign the loop variable to another variable declared inside the statement block
3 Filtered: prints the name of each element of an integer array that is less than 5
4 Filter string by its length
5 prints strings where each element has the second letter "i".
6 Query string value by String.StartsWith
7 Query Using the Query Expression Syntax
8 Query with an Exception
9 To remove all vowels from a string.
10 Two where clauses
11 Use && in where clause
12 Use string method in where clause
13 use where clause in a while loop
14 Use where to filer object list
15 where clause
16 Where clause with string method and return IEnumerable object
17 Where Prototype

A Query Using the Standard Dot Notation Syntax

 

using System;
using System.Linq;
using System.Collections;
using System.Collections.Generic;
public class MainClass {
    public static void Main() {
        string[] names = { "A1", "B123", "C123123", "E", "W" };
        IEnumerable<string> sequence = names
         .Where(n => n.Length < 6)
         .Select(n => n);
        foreach (string name in sequence) {
            Console.WriteLine("{0}", name);
        }
    }
}

Assign the loop variable to another variable declared inside the statement block

 
using System;
using System.Collections.Generic;
using System.Linq;
public class MainClass {
    public static void Main() {
        IEnumerable<char> vowels = "aeiou";
        IEnumerator<char> rator = vowels.GetEnumerator();
        IEnumerable<char> query = "Not what you might expect";

        foreach (char vowel in "aeiou") {
            char temp = vowel;
            query = query.Where(c => c != temp);
        }
    }
}

Filtered: prints the name of each element of an integer array that is less than 5

 
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
public class MainClass {
    public static void Main() {
        int[] numbers = { 5, 4, 1, 3};
        string[] digits = { "zero", "one", "two", "three"};
        var lowNums =
            from n in numbers
            where n < 5
            select digits[n];
        Console.WriteLine("Numbers < 5:");
        foreach (var num in lowNums) {
            Console.WriteLine(num);
        }
    }
}

Filter string by its length

 
using System;
using System.Collections.Generic;
using System.Linq;
class LinqDemo {
    static void Main() {
        string[] names = { "Tom", "Dick", "Harry" };

        IEnumerable<string> filteredNames = names.Where(n => n.Length >= 4);
        foreach (string name in filteredNames) Console.Write(name + "|");
    }
}

prints strings where each element has the second letter "i".

 
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
public class MainClass {
    public static void Main() {
        string[] digits = { "ziro", "one", "two", "three"};
        var reversedIDigits = (
            from d in digits
            where d[1] == "i"
            select d)
            .Reverse();
        foreach (var d in reversedIDigits) {
            Console.WriteLine(d);
        }
    }
}

Query string value by String.StartsWith

 
using System;
using System.Linq;
using System.Collections;
using System.Collections.Generic;
public class MainClass {
    public static void Main() {
        string[] presidents = {"Ad", "Ar", "Bu", "B", "C", "C"};
        string president = presidents.Where(p => p.StartsWith("Ad")).First();
        Console.WriteLine(president);
    }
}

Query Using the Query Expression Syntax

 

using System;
using System.Linq;
using System.Collections;
using System.Collections.Generic;
public class MainClass {
    public static void Main() {
        string[] names = { "A123123", "B123", "C123123", "E123", "W" };
        IEnumerable<string> sequence = from n in names
                                       where n.Length < 6
                                       select n;
        foreach (string name in sequence) {
            Console.WriteLine("{0}", name);
        }
    }
}

Query with an Exception

 

using System;
using System.Linq;
using System.Collections;
using System.Collections.Generic;
public class MainClass {
    public static void Main() {
        string[] presidents = {"AAAA", "aaaa", "bacDert", "B1234", "Carter"};
        IEnumerable<string> items = presidents.Where(s => Char.IsLower(s[4]));
        Console.WriteLine("After the query.");
        foreach (string item in items)
            Console.WriteLine(item);
    }
}

To remove all vowels from a string.

 
using System;
using System.Collections.Generic;
using System.Linq;
public class MainClass {
    public static void Main() {
        IEnumerable<char> query = "Not what you might expect";
        query = query.Where(c => c != "a");
        query = query.Where(c => c != "e");
        query = query.Where(c => c != "i");
        query = query.Where(c => c != "o");
        query = query.Where(c => c != "u");
        foreach (char c in query) Console.Write(c); 
    }
}

Two where clauses

 
using System;
using System.Collections;
using System.Collections.Generic;
using System.Text;
using System.Linq;
class Employee {
    int _id;
    int _idRole;
    string _lastName;
    string _firstName;
    public int ID {
        get { return _id; }
        set { _id = value; }
    }
    public int IDRole {
        get { return _idRole; }
        set { _idRole = value; }
    }
    public string LastName {
        get { return _lastName; }
        set { _lastName = value; }
    }
    public string FirstName {
        get { return _firstName; }
        set { _firstName = value; }
    }
}
class Salary {
    int _id;
    int _year;
    double _salary;
    public int ID {
        get { return _id; }
        set { _id = value; }
    }
    public int Year {
        get { return _year; }
        set { _year = value; }
    }
    public double SalaryPaid {
        get { return _salary; }
        set { _salary = value; }
    }
}
public class MainClass {
    public static void Main() {
        List<Employee> people = new List<Employee> {
              new Employee  { ID = 1, IDRole = 1, LastName = "A", FirstName = "B"},
              new Employee  { ID = 2, IDRole = 2, LastName = "G", FirstName = "T"}
            };
        List<Salary> salaries = new List<Salary> {
               new Salary { ID = 1, Year = 2004, SalaryPaid = 10000.00 },
               new Salary { ID = 1, Year = 2005, SalaryPaid = 15000.00 },
               new Salary { ID = 1, Year = 2005, SalaryPaid = 15000.00 }
            };
        IEnumerable<Salary> q = from p in people
                                where p.ID == 1
                                from s in salaries
                                where s.ID == p.ID
                                select s;

    }
}

Use && in where clause

 
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
public class MainClass {
    public static void Main() {
        List<Product> products = GetProductList();
        var expensiveInStockProducts =
            from p in products
            where p.UnitsInStock > 0 && p.UnitPrice > 3.00M
            select p;
        foreach (var product in expensiveInStockProducts) {
            Console.WriteLine(product.ProductName);
        }
    }
    static List<Product> GetProductList() {
        List<Product> empTree = new List<Product>();
        empTree.Add(new Product { ProductName = "A", Category = "O", UnitPrice = 12, UnitsInStock = 5, Total = 36, OrderDate = new DateTime(2005, 1, 1), Id = 1 });
        empTree.Add(new Product { ProductName = "B", Category = "O", UnitPrice = 2, UnitsInStock = 4, Total = 35, OrderDate = new DateTime(2005, 1, 1), Id = 1 });
        empTree.Add(new Product { ProductName = "C", Category = "O", UnitPrice = 112, UnitsInStock = 3, Total = 34, OrderDate = new DateTime(2005, 1, 1), Id = 1 });
        empTree.Add(new Product { ProductName = "D", Category = "O", UnitPrice = 112, UnitsInStock = 0, Total = 33, OrderDate = new DateTime(2005, 1, 1), Id = 1 });
        empTree.Add(new Product { ProductName = "E", Category = "O", UnitPrice = 1112, UnitsInStock = 2, Total = 32, OrderDate = new DateTime(2005, 1, 1), Id = 1 });
        empTree.Add(new Product { ProductName = "F", Category = "O", UnitPrice = 11112, UnitsInStock = 0, Total = 31, OrderDate = new DateTime(2005, 1, 1), Id = 1 });
        return empTree;
    }
}
class Product : IComparable<Product> {
    public string ProductName { get; set; }
    public string Category { get; set; }
    public int UnitPrice { get; set; }
    public int UnitsInStock { get; set; }
    public int Total { get; set; }
    public DateTime OrderDate { get; set; }
    public int Id { get; set; }
    public override string ToString() {
        return String.Format("Id: {0}, Name: {1} , Category: {3}", this.Id, this.ProductName, this.Category);
    }
    int IComparable<Product>.rupareTo(Product other) {
        if (other == null)
            return 1;
        if (this.Id > other.Id)
            return 1;
        if (this.Id < other.Id)
            return -1;
        return 0;
    }
}

Use string method in where clause

 

using System;
using System.Linq;
public class MainClass {
    public static void Main() {
        string[] greetings = { "hello world", "hello LINQ", "hello" };
        var items =
         from s in greetings
         where s.EndsWith("LINQ")
         select s;
        foreach (var item in items)
            Console.WriteLine(item);
    }
}

use where clause in a while loop

 
using System;
using System.Collections.Generic;
using System.Linq;
public class MainClass {
    public static void Main() {
        IEnumerable<char> vowels = "aeiou";
        IEnumerator<char> rator = vowels.GetEnumerator();
        IEnumerable<char> query = "Not what you might expect";
        char vowel;
        while (rator.MoveNext()) {
            vowel = rator.Current;
            query = query.Where(c => c != vowel);
        }
    }
}

Use where to filer object list

 
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
public class MainClass {
    public static void Main() {
        List<Product> products = GetProductList();
        var soldOutProducts =
            from p in products
            where p.UnitsInStock == 0
            select p;
        Console.WriteLine("Sold out products:");
        foreach (var product in soldOutProducts) {
            Console.WriteLine("{0} is sold out!", product.ProductName);
        }
    }
    static List<Product> GetProductList() {
        List<Product> empTree = new List<Product>();
        empTree.Add(new Product { ProductName = "A", Category = "O", UnitPrice = 12, UnitsInStock = 5, Total = 36, OrderDate = new DateTime(2005, 1, 1), Id = 1 });
        empTree.Add(new Product { ProductName = "B", Category = "O", UnitPrice = 2, UnitsInStock = 4, Total = 35, OrderDate = new DateTime(2005, 1, 1), Id = 1 });
        empTree.Add(new Product { ProductName = "C", Category = "O", UnitPrice = 112, UnitsInStock = 3, Total = 34, OrderDate = new DateTime(2005, 1, 1), Id = 1 });
        empTree.Add(new Product { ProductName = "D", Category = "O", UnitPrice = 112, UnitsInStock = 0, Total = 33, OrderDate = new DateTime(2005, 1, 1), Id = 1 });
        empTree.Add(new Product { ProductName = "E", Category = "O", UnitPrice = 1112, UnitsInStock = 2, Total = 32, OrderDate = new DateTime(2005, 1, 1), Id = 1 });
        empTree.Add(new Product { ProductName = "F", Category = "O", UnitPrice = 11112, UnitsInStock = 0, Total = 31, OrderDate = new DateTime(2005, 1, 1), Id = 1 });
        return empTree;
    }
}
class Product : IComparable<Product> {
    public string ProductName { get; set; }
    public string Category { get; set; }
    public int UnitPrice { get; set; }
    public int UnitsInStock { get; set; }
    public int Total { get; set; }
    public DateTime OrderDate { get; set; }
    public int Id { get; set; }
    public override string ToString() {
        return String.Format("Id: {0}, Name: {1} , Category: {3}", this.Id, this.ProductName, this.Category);
    }
    int IComparable<Product>.rupareTo(Product other) {
        if (other == null)
            return 1;
        if (this.Id > other.Id)
            return 1;
        if (this.Id < other.Id)
            return -1;
        return 0;
    }
}

where clause

 
using System;
using System.Collections;
using System.Collections.Generic;
using System.Text;
using System.Linq;
using System.Reflection;
class Person {
    int _id;
    int _idRole;
    string _lastName;
    string _firstName;
    public int ID {
        get { return _id; }
        set { _id = value; }
    }
    public int IDRole {
        get { return _idRole; }
        set { _idRole = value; }
    }
    public string LastName {
        get { return _lastName; }
        set { _lastName = value; }
    }
    public string FirstName {
        get { return _firstName; }
        set { _firstName = value; }
    }
}
class Program {
    static void Main(string[] args) {
        List<Person> people = new List<Person> {
              new Person  { ID = 1, IDRole = 1, LastName = "A", FirstName = "B"},
              new Person  { ID = 2, IDRole = 2, LastName = "G", FirstName = "T"},
              new Person  { ID = 3, IDRole = 2, LastName = "G", FirstName = "M"},
              new Person  { ID = 4, IDRole = 3, LastName = "C", FirstName = "G"}
            };
        var query = people.Where((p, index) => p.IDRole == index);
    }
}

Where clause with string method and return IEnumerable object

 
using System;
using System.Linq;
using System.Collections;
using System.Collections.Generic;
public class MainClass {
    public static void Main() {

        string[] presidents = {"AA", "A", "AAA", "B", "Ca", "C"};
        IEnumerable<string> items = presidents.Where(p => p.StartsWith("A"));
        foreach (string item in items)
            Console.WriteLine(item);
    }
}

Where Prototype

 
using System;
using System.Linq;
using System.Collections;
using System.Collections.Generic;
public class MainClass {
    public static void Main() {
        string[] presidents = {"A", "Ar", "B", "Bu", "C", "Cleveland"};
        IEnumerable<string> sequence = presidents.Where(p => p.StartsWith("C"));
        foreach (string s in sequence)
            Console.WriteLine("{0}", s);
    }
}

Csharp/C Sharp/LINQ/where

Содержание

A Query Using the Standard Dot Notation Syntax

Assign the loop variable to another variable declared inside the statement block

Filtered: prints the name of each element of an integer array that is less than 5

Filter string by its length

prints strings where each element has the second letter "i".

Query string value by String.StartsWith

Query Using the Query Expression Syntax

Query with an Exception

To remove all vowels from a string.

Two where clauses

Use && in where clause

Use string method in where clause

use where clause in a while loop

Use where to filer object list

where clause

Where clause with string method and return IEnumerable object

Where Prototype

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