Csharp/CSharp Tutorial/LINQ/Count
Содержание
Conditional Count
<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, 8, 6, 7, 2, 0 }; int oddNumbers = numbers.Count(n => n % 2 == 1); Console.WriteLine("There are {0} odd numbers in the list.", oddNumbers); }
}</source>
Count with string operator
<source lang="csharp">using System; using System.Linq; using System.Collections; using System.Collections.Generic; public class MainClass {
public static void Main() { string[] presidents = {"G", "H", "a", "H", "over", "Jack"}; int count = presidents.Count(s => s.StartsWith("H")); Console.WriteLine(count); }
}</source>
Count with string value
<source lang="csharp">using System; using System.Linq; using System.Collections; using System.Collections.Generic; public class MainClass {
public static void Main() { string[] presidents = {"G", "H", "a", "H", "over", "Jack"}; int count = presidents.Count(); Console.WriteLine(count); }
}</source>
Nested Count
<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 orderCounts = from c in customers select new { c.CustomerId, OrderCount = c.Orders.Count() }; Console.Write(orderCounts); } 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>
Numeric Aggregates: count
<source lang="csharp">using System; using System.Collections.Generic; using System.Linq; using System.Text;
class Program { static void Main(string[] args) { Random generator = new Random(0); int[] numbers = new int[1000]; for (int i = 0; i < 1000; i++) { numbers[i] = generator.Next(); } var queryResults = from n in numbers where n > 100 select n; Console.WriteLine("Count of Numbers > 100"); Console.WriteLine(queryResults.Count()); } }</source>
The aggregation operators return a scalar value
<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 }; int count = numbers.Count(); int min = numbers.Min(); }
}</source>
Use Aggregate Operators: Count
<source lang="csharp">using System; using System.Collections.Generic; using System.Linq; using System.Text; public class MainClass {
public static void Main() { int[] factorsOf300 = { 2, 2, 3, 5, 5 }; int uniqueFactors = factorsOf300.Distinct().Count(); Console.WriteLine("There are {0} unique factors of 300.", uniqueFactors); }
}</source>