Csharp/CSharp Tutorial/LINQ/Group

Group Query

<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 Program
   {
       static void Main(string[] args)
       {
           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 queryResults =
               from c in customers
               group c by c.Region into cg
               select new { TotalSales = cg.Sum(c => c.Sales), Region = cg.Key }
              ;
           var orderedResults =
               from cg in queryResults
               orderby cg.TotalSales descending
               select cg
            ;
           foreach (var item in orderedResults)
           {
               Console.WriteLine(item.TotalSales + "\t: " + item.Region);
           }
       }
   }</source>

Group words by length

<source lang="csharp">using System; using System.Linq; class HelloWorld {

   static void Main() {
       string[] words = { "A", "ss", "w", "ccc", "a" };
       var groups =
         from word in words
         orderby word ascending
         group word by word.Length into lengthGroups
         orderby lengthGroups.Key descending
         select new { Length = lengthGroups.Key, Words = lengthGroups };
       foreach (var group in groups) {
           Console.WriteLine("Words of length " + group.Length);
           foreach (string word in group.Words)
               Console.WriteLine("  " + word);
       }
   }

}</source>

Select from a Group

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

   public static void Main() {
       var query = from m in typeof(int).GetMethods() select m.Name;
       
       var q = from m in typeof(int).GetMethods()
               group m by m.Name into gb
               select new { Name = gb.Key };
   }

}</source>

Using group to group all employees by department

<source lang="csharp">using System; using System.Collections.Generic; using System.Linq; using System.Text; public class Tree<TreeNode> : IEnumerable<TreeNode> where TreeNode : IComparable<TreeNode> {

   public Tree(TreeNode nodeValue) {
       this.NodeData = nodeValue;
       this.LeftTree = null;
       this.RightTree = null;
   }
   public void Insert(TreeNode newItem) {
       TreeNode currentNodeValue = this.NodeData;
       if (currentNodeValue.rupareTo(newItem) > 0) {
           if (this.LeftTree == null) {
               this.LeftTree = new Tree<TreeNode>(newItem);
           } else {
               this.LeftTree.Insert(newItem);
           }
       } else {
           if (this.RightTree == null) {
               this.RightTree = new Tree<TreeNode>(newItem);
           } else {
               this.RightTree.Insert(newItem);
           }
       }
   }
   public void WalkTree() {
       if (this.LeftTree != null) {
           this.LeftTree.WalkTree();
       }
       Console.WriteLine(this.NodeData.ToString());
       if (this.RightTree != null) {
           this.RightTree.WalkTree();
       }
   }
   public TreeNode NodeData { get; set; }
   public Tree<TreeNode> LeftTree { get; set; }
   public Tree<TreeNode> RightTree { get; set; }

   IEnumerator<TreeNode> IEnumerable<TreeNode>.GetEnumerator() {
       if (this.LeftTree != null) {
           foreach (TreeNode item in this.LeftTree) {
               yield return item;
           }
       }
       yield return this.NodeData;
       if (this.RightTree != null) {
           foreach (TreeNode item in this.RightTree) {
               yield return item;
           }
       }
   }
   System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() {
       throw new NotImplementedException();
   }

} class Employee : IComparable<Employee> {

   public string FirstName { get; set; }
   public string LastName { get; set; }
   public string Department { get; set; }
   public int Id { get; set; }
   public override string ToString() {
       return String.Format("Id: {0}, Name: {1} {2}, Dept: {3}", this.Id, this.FirstName, this.LastName, this.Department);
   }
   int IComparable<Employee>.rupareTo(Employee other) {
       if (other == null)
           return 1;
       if (this.Id > other.Id)
           return 1;
       if (this.Id < other.Id)
           return -1;
       return 0;
   }

} class Program {

   static void Main() {
       Tree<Employee> empTree = new Tree<Employee>(new Employee { Id = 1, FirstName = "Janet", LastName = "Gates", Department = "IT" });
       empTree.Insert(new Employee { Id = 2, FirstName = "O", LastName = "G", Department = "Marketing" });
       empTree.Insert(new Employee { Id = 4, FirstName = "K", LastName = "H", Department = "IT" });
       empTree.Insert(new Employee { Id = 6, FirstName = "L", LastName = "H", Department = "Sales" });
       empTree.Insert(new Employee { Id = 3, FirstName = "E", LastName = "L", Department = "Sales" });
       empTree.Insert(new Employee { Id = 5, FirstName = "D", LastName = "L", Department = "Marketing" });
       var employeesByDept = from e in empTree group e by e.Department;
       foreach (var dept in employeesByDept)
       {
           Console.WriteLine("Department: {0}", dept.Key);
           foreach (var emp in dept)
           {
               Console.WriteLine("\t{0} {1}", emp.FirstName, emp.LastName);
           }
       }
   }

}</source>