Csharp/CSharp Tutorial/LINQ/ToDictionary

Calling the First ToDictionary Prototype

using System;
using System.Linq;
using System.Collections;
using System.Collections.Generic;
public class Employee {
    public int id;
    public string firstName;
    public string lastName;
    public static ArrayList GetEmployeesArrayList() {
        ArrayList al = new ArrayList();
        al.Add(new Employee { id = 1, firstName = "J", lastName = "R" });
        al.Add(new Employee { id = 2, firstName = "W", lastName = "G" });
        al.Add(new Employee { id = 3, firstName = "A", lastName = "H" });
        al.Add(new Employee { id = 4, firstName = "D", lastName = "L" });
        al.Add(new Employee { id = 101, firstName = "K", lastName = "F" });
        return (al);
    }
    public static Employee[] GetEmployeesArray() {
        return ((Employee[])GetEmployeesArrayList().ToArray());
    }
}
public class MainClass {
    public static void Main() {
        Dictionary<int, Employee> eDictionary = Employee.GetEmployeesArray().ToDictionary(k => k.id);
        Employee e = eDictionary[2];
        Console.WriteLine("Employee whose id == 2 is {0} {1}", e.firstName, e.lastName);
    }
}

Convert query to Dictionary

using System;
using System.Collections;
using System.Collections.Generic;
using System.Text;
using System.Linq;
public class MainClass{
   public static void Main(){
            var q = from m in typeof(int).GetMethods()
                    group m by m.Name into gb
                    select gb;
            Dictionary<string, int> d = q.ToDictionary(k => k.Key, k => k.Count());
   }
}

Second ToDictionary

using System;
using System.Linq;
using System.Collections;
using System.Collections.Generic;
public class Employee2 {
    public string id;
    public string firstName;
    public string lastName;
    public static ArrayList GetEmployeesArrayList() {
        ArrayList al = new ArrayList();
        al.Add(new Employee2 { id = "1", firstName = "J", lastName = "R" });
        al.Add(new Employee2 { id = "2", firstName = "W", lastName = "G" });
        al.Add(new Employee2 { id = "3", firstName = "A",lastName = "H"});
        al.Add(new Employee2 { id = "4", firstName = "D", lastName = "L" });
        al.Add(new Employee2 { id = "101", firstName = "K", lastName = "F" });
        return (al);
    }
    public static Employee2[] GetEmployeesArray() {
        return ((Employee2[])GetEmployeesArrayList().ToArray(typeof(Employee2)));
    }
}
public class MyStringifiedNumberComparer : IEqualityComparer<string> {
    public bool Equals(string x, string y) {
        return (Int32.Parse(x) == Int32.Parse(y));
    }
    public int GetHashCode(string obj) {
        return Int32.Parse(obj).ToString().GetHashCode();
    }
}
public class MainClass {
    public static void Main() {
        Dictionary<string, Employee2> eDictionary = Employee2.GetEmployeesArray().ToDictionary(k => k.id, new MyStringifiedNumberComparer());
        Employee2 e = eDictionary["2"];
        Console.WriteLine("Employee whose id == \"2\" : {0} {1}", e.firstName, e.lastName);
        e = eDictionary["000002"];
        Console.WriteLine("Employee whose id == \"000002\" : {0} {1}",e.firstName, e.lastName);
    }
}

ToDictionary: convert query result to Dictionary

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
public class MainClass {
    public static void Main() {
        var scoreRecords = new[] { new {Name = "A", Score = 50},
                                new {Name = "B" , Score = 40},
                                new {Name = "C", Score = 45}
                              };
        var scoreRecordsDict = scoreRecords.ToDictionary(sr => sr.Name);
        Console.WriteLine("Bob"s score: {0}", scoreRecordsDict["Bob"]);
    }
}

ToDictionary for an object list

using System;
using System.Linq;
using System.Collections;
using System.Collections.Generic;
public class Employee {
    public int id;
    public string firstName;
    public string lastName;
    public static ArrayList GetEmployeesArrayList() {
        ArrayList al = new ArrayList();
        al.Add(new Employee { id = 1, firstName = "J", lastName = "R" });
        al.Add(new Employee { id = 2, firstName = "W", lastName = "G" });
        al.Add(new Employee { id = 3, firstName = "A", lastName = "H" });
        al.Add(new Employee { id = 4, firstName = "D", lastName = "L" });
        al.Add(new Employee { id = 101, firstName = "K", lastName = "F" });
        return (al);
    }
    public static Employee[] GetEmployeesArray() {
        return ((Employee[])GetEmployeesArrayList().ToArray());
    }
}
public class MainClass {
    public static void Main() {
        Dictionary<int, string> eDictionary = Employee.GetEmployeesArray().ToDictionary(k => k.id, i => string.Format("{0} {1}",i.firstName, i.lastName));
        string name = eDictionary[2];
        Console.WriteLine("Employee whose id == 2 is {0}", name);
    }
}

ToDictionary with IEqualityComparer

using System;
using System.Linq;
using System.Collections;
using System.Collections.Generic;
public class Employee2 {
    public string id;
    public string firstName;
    public string lastName;
    public static ArrayList GetEmployeesArrayList() {
        ArrayList al = new ArrayList();
        al.Add(new Employee2 { id = "1", firstName = "J", lastName = "R" });
        al.Add(new Employee2 { id = "2", firstName = "W", lastName = "G" });
        al.Add(new Employee2 { id = "3", firstName = "A", lastName = "H"});
        al.Add(new Employee2 { id = "4", firstName = "D", lastName = "L" });
        al.Add(new Employee2 { id = "101", firstName = "K", lastName = "F" });
        return (al);
    }
    public static Employee2[] GetEmployeesArray() {
        return ((Employee2[])GetEmployeesArrayList().ToArray(typeof(Employee2)));
    }
}
public class MyStringifiedNumberComparer : IEqualityComparer<string> {
    public bool Equals(string x, string y) {
        return (Int32.Parse(x) == Int32.Parse(y));
    }
    public int GetHashCode(string obj) {
        return Int32.Parse(obj).ToString().GetHashCode();
    }
}
public class MainClass {
    public static void Main() {
        Dictionary<string, string> eDictionary = Employee2.GetEmployeesArray()
          .ToDictionary(k => k.id,i => string.Format("{0} {1}",i.firstName, i.lastName),new MyStringifiedNumberComparer());
        string name = eDictionary["2"];
        Console.WriteLine("Employee whose id == \"2\" : {0}", name);
        name = eDictionary["000002"];
        Console.WriteLine("Employee whose id == \"000002\" : {0}", name);
    }
}