Csharp/CSharp Tutorial/LINQ/Take
Содержание
Get the first four element in the list
<source lang="csharp">using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Linq.Expressions; using System.Xml.Linq;
class Program { static void Main(string[] args) { int[] integers = { 1, 6, 2, 27, 10 }; IEnumerable<int> firstFourNumbers = integers.Take(4); Console.WriteLine("First 4 numbers:"); foreach (var num in firstFourNumbers) { Console.WriteLine(num); } } }</source>
Nested Take
<source lang="csharp">using System; using System.Collections.Generic; using System.Linq; using System.Text; public class MainClass {
public static void Main() { List<Customer> customers = GetCustomerList(); var first3WAOrders = ( from c in customers from o in c.Orders where c.Region == "R1" select new { c.CustomerId, o.Id, o.OrderDate }) .Take(3); Console.WriteLine("First 3 orders in WA:"); foreach (var order in first3WAOrders) { Console.WriteLine(order); } } static List<Customer> GetCustomerList() { 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 }); List<Customer> l = new List<Customer>(); l.Add(new Customer { CompanyName = "A", Region = "R1", UnitsInStock = 1, Orders = empTree, CustomerId = 0 }); l.Add(new Customer { CompanyName = "B", Region = "R2", UnitsInStock = 2, Orders = empTree, CustomerId = 1 }); l.Add(new Customer { CompanyName = "C", Region = "R3", UnitsInStock = 3, Orders = empTree, CustomerId = 2 }); l.Add(new Customer { CompanyName = "D", Region = "R4", UnitsInStock = 4, Orders = empTree, CustomerId = 3 }); l.Add(new Customer { CompanyName = "E", Region = "R5", UnitsInStock = 5, Orders = empTree, CustomerId = 4 }); return l; }
} class Customer : IComparable<Customer> {
public string CompanyName { get; set; } public string Region { get; set; } public List<Product> Orders { get; set; } public int UnitsInStock { get; set; } public int CustomerId { get; set; } public override string ToString() { return String.Format("Id: {0}, Name: {1}, Region: {3}", this.CustomerId, this.rupanyName, this.Region); } int IComparable<Customer>.rupareTo(Customer other) { if (other == null) return 1; if (this.CustomerId > other.CustomerId) return 1; if (this.CustomerId < other.CustomerId) return -1; return 0; }
} 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; }
}</source>
Partitioning Operators: uses Take to generate a sequence of the first three elements of an integer array.
<source lang="csharp">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, 9}; var first3Numbers = numbers.Take(3); Console.WriteLine("First 3 numbers:"); foreach (var n in first3Numbers) { Console.WriteLine(n); } }
}</source>
Take and SelectMany
<source lang="csharp">using System; using System.Linq; using System.Collections; using System.Collections.Generic; public class MainClass {
public static void Main() { string[] presidents = {"Aaa", "Art", "Buch", "Bushman", "Carter", "land"}; IEnumerable<char> chars = presidents.Take(5).SelectMany(s => s.ToArray()); foreach (char ch in chars) Console.WriteLine(ch); }
}</source>
Take method
<source lang="csharp">using System; using System.Linq; using System.Collections; using System.Collections.Generic; public class MainClass {
public static void Main() { string[] presidents = {"A", "A", "B", "Bu", "Car", "land"}; IEnumerable<string> items = presidents.Take(5); foreach (string item in items) Console.WriteLine(item); }
}</source>
Take operator outputs the first x elements, discarding the rest
<source lang="csharp">using System; using System.Collections.Generic; using System.Linq; public class MainClass {
public static void Main() { int[] numbers = { 10, 9, 8, 7, 6 }; IEnumerable<int> firstThree = numbers.Take(3); // { 10, 9, 8 } }
}</source>
Use Take
<source lang="csharp">using System; using System.Collections; using System.Collections.Generic; using System.Text; using System.Linq; public class MainClass{
public static void Main(){ int[] numbers = { 1, 2, 3, 4, 5, 6, 7, 8, 9 }; var query = numbers.Take(5); var query2 = numbers.Skip(5); }
}</source>