Csharp/CSharp Tutorial/LINQ/Count

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>