Csharp/CSharp Tutorial/LINQ/Union

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prints the unique elements of two integer arrays

<source lang="csharp">using System; using System.Collections.Generic; using System.Linq; using System.Text; public class MainClass {

   public static void Main() {
       int[] numbersA = { 0, 2, 4, 5, 6, 8, 9 };
       int[] numbersB = { 1, 3, 5, 7, 8 };
       var uniqueNumbers = numbersA.Union(numbersB);
       Console.WriteLine("Unique numbers from both arrays:");
       foreach (var n in uniqueNumbers) {
           Console.WriteLine(n);
       }
   }

}</source>

prints unique letters from Product and Customer names

<source lang="csharp">using System; using System.Collections.Generic; using System.Linq; using System.Text; public class MainClass {

   public static void Main() {
       List<Product> products = GetProductList();
       List<Customer> customers = GetCustomerList();
       var productFirstChars =
           from p in products
           select p.ProductName[0];
       var customerFirstChars =
           from c in customers
           select c.rupanyName[0];
       var uniqueFirstChars = productFirstChars.Union(customerFirstChars);
       Console.WriteLine("Unique first letters from Product names and Customer names:");
       foreach (var ch in uniqueFirstChars) {
           Console.WriteLine(ch);
       }
   }
   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;
   }
   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>

Set Operators: Union

<source lang="csharp">using System; using System.Collections.Generic; using System.Linq; using System.Text;

   class Customer
   {
       public string ID { get; set; }
       public string City { get; set; }
       public string Country { get; set; }
       public string Region { get; set; }
       public decimal Sales { get; set; }
   }
   class Order
   {
       public string ID { get; set; }
       public decimal Amount { get; set; }
   }
   class Program
   {
       static void Main(string[] args)
       {
           List<Order> orders = new List<Order> {
             new Order { ID="R", Amount=900 },
             new Order { ID="S", Amount=1000 },
             new Order { ID="T", Amount=1100 }
           };
           List<Customer> customers = new List<Customer> {
             new Customer { ID="Q", City="London", Country="UK", Region="Europe", Sales=8000 },
             new Customer { ID="R", City="Beijing", Country="China", Region="Asia", Sales=9000 },
             new Customer { ID="T", City="Lima", Country="Peru", Region="South America", Sales=2002 }
          };
           var customerIDs = from c in customers select c.ID;
           var orderIDs = from o in orders select o.ID;
           var allCustomerOrderIDs = orderIDs.Union(customerIDs);
           foreach (var item in allCustomerOrderIDs)
           {
               Console.Write("{0} ", item);
           }            
       }
   }</source>

Union does appends one sequence to another with duplicates removed:

<source lang="csharp">using System; using System.Collections.Generic; using System.Linq; public class MainClass {

   public static void Main() {
       int[] seq1 = { 1, 2, 3 };
       int[] seq2 = { 3, 4, 5 };
       IEnumerable<int> concat = seq1.Concat(seq2);    //  { 1, 2, 3, 3, 4, 5 }
       IEnumerable<int> union = seq1.Union(seq2);     //  { 1, 2, 3, 4, 5 }
   }

}</source>

Union 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 = {"ant", "arding", "arrison", "eyes", "over", "ackson"};
       IEnumerable<string> first = presidents.Take(5);
       IEnumerable<string> second = presidents.Skip(4);
       IEnumerable<string> concat = first.Concat<string>(second);
       IEnumerable<string> union = first.Union<string>(second);
       Console.WriteLine("The count of the array is: " + presidents.Count());
       Console.WriteLine("The count of the first sequence is: " + first.Count());
       Console.WriteLine("The count of the second sequence is: " + second.Count());
       Console.WriteLine("The count of the concat sequence is: " + concat.Count());
       Console.WriteLine("The count of the union sequence is: " + union.Count());
   }

}</source>

Use Linq to union two arrays

<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, 1, 3, 3};
           int[] numbers2 = {1, 2, 3, 4};
           Console.Write(numbers.Union(numbers2));
  }

}</source>