C# Generic Collections Part 6: Comparison Delegate

Comparison delegate is used to sort or order the data inside a collection. It takes two parameters as generic input type and return type should always be int. This is how we can declare Comparison delegate.

Code:

1. using System;  
2. using System.Collections.Generic;  
3. using System.Linq;  
4. using System.Text;  
5. using System.Threading.Tasks;  
6.   
7. namespace genericUserDefined  
8. {  
9.     public class Employee : IComparable<Employee>  
10.     {  
11.         public int eid { get; set; }  
12.         public string first_name { get; set; }  
13.         public string last_name { get; set; }  
14.         public string department { get; set; }  
15.         public double salary { get; set; }  
16.   
17.         public int CompareTo(Employee other)  
18.         {  
19.             if (this.eid > other.eid)  
20.                 return 1;  
21.             else if (this.eid < other.eid)  
22.                 return -1;  
23.             else  
24.                 return 0;  
25.         }  
26.     }  
27.     public class compareEmployee : IComparer<Employee>  
28.     {  
29.   
30.         public int Compare(Employee x, Employee y)  
31.         {  
32.             if (x.salary > y.salary)  
33.                 return 1;  
34.             else if (x.salary < y.salary)  
35.                 return -1;  
36.             else  
37.                 return 0;  
38.         }  
39.     }  
40. }  
41.   
42.   
43. //Main class  
44.   
45. using System;  
46. using System.Collections.Generic;  
47. using System.Linq;  
48. using System.Text;  
49. using System.Threading.Tasks;  
50.   
51. namespace genericUserDefined  
52. {  
53.     class Program  
54.     {  
55.   
56.         public static int compareNames(Employee n1, Employee n2)  
57.         {  
58.             return n1.first_name.CompareTo(n2.first_name);  
59.         }  
60.   
61.         static void Main(string[] args)  
62.         {  
63.             List<Employee> elist = new List<Employee>();  
64.   
65.             Employee e1 = new Employee();  
66.             e1.eid = 101;  
67.             e1.first_name = "Sujan";  
68.             e1.last_name = "Hasan";  
69.             e1.department = "IT";  
70.             e1.salary = 55000.00;  
71.   
72.             elist.Add(e1);  
73.   
74.             Employee e2 = new Employee();  
75.             e2.eid = 102;  
76.             e2.first_name = "Shakil";  
77.             e2.last_name = "Sorker";  
78.             e2.department = "Networking";  
79.             e2.salary = 175000.00;  
80.   
81.             elist.Add(e2);  
82.   
83.             Employee e3 = new Employee();  
84.             e3.eid = 100;  
85.             e3.first_name = "Shimul";  
86.             e3.last_name = "Hossain";  
87.             e3.department = "Marketing";  
88.             e3.salary = 75000.50;  
89.             elist.Add(e3);  
90.   
91.               
92.   
93.             print(elist);  
94.             Console.WriteLine("\nAfter sorting the value with respect of employee id:\n");  
95.             elist.Sort();  
96.             print(elist);  
97.   
98.             Console.WriteLine("\nSorting with respect to salary:\n");  
99.             compareEmployee obj = new compareEmployee();  
100.             elist.Sort(obj);  
101.             print(elist);  
102.   
103.             Comparison<Employee>obj1=new Comparison<Employee>(compareNames);//Using comparison delegate  
104.             Console.WriteLine("\nSorting with respect to first_name:\n");  
105.             elist.Sort(obj1);  
106.             print(elist);  
107.   
108.             Console.ReadKey();  
109.         }  
110.         public static void print(List<Employee> emp)  
111.         {  
112.             foreach (Employee obj in emp)  
113.             {  
114.                 Console.WriteLine(obj.eid+" "+obj.first_name+" "+obj.last_name+" "+obj.department+" "+obj.salary);  
115.             }  
116.         }  
117.     }  
118. }