Csharp/CSharp Tutorial/LINQ/Group

Group Query

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);
            }
        }
    }

Group words by length

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);
        }
    }
}

Select from a Group

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 };
    }
}

Using group to group all employees by department

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);
            }
        }
    }
}