The List(T) represents a strongly typed collection of objects which is highly optimized for providing maximum performance and can be accessed using an index. This class provides methods to loop, filter, sort and manipulate collections. For those interested, the non-generic version of this class is the ArrayList class.
In this article we will see some common operations like search, sort, loop and manipulating lists. Since this article focuses on demonstrating some common operations of the Generics List(T) class, I have decided to keep the sample as simple as possible and will go ahead with a console application. I assume you are familiar with the features of C# 2.0 and VB.NET and understand Generics in particular.
To create a console application, open Visual Studio 2005/2008 > File > New Project > Select your desired Language and in the template pane, select Console application.
I will be using a collection of a ‘Person’ class and store it in the List(T). To add a Person class to your application, right click your project > Add > Class > rename the class to Person.cs or Person.vb. Add the following properties to the Person class:
using System;
using System.Collections.Generic;
using System.Text;
namespace CommonGenericOperations
{
public class Person
{
public Person()
{
}
public Person(int id, string first_name, string mid_name, string last_name, short age, char sex)
{
this.p_id = id;
this.first_name = first_name;
this.mid_name = mid_name;
this.last_name = last_name;
this.p_age = age;
this.p_sex = sex;
}
private int p_id = -1;
private string first_name = String.Empty;
private string mid_name = String.Empty;
private string last_name = String.Empty;
private short p_age = 0;
private char? p_sex = null;
public int ID
{
get
{
return p_id;
}
set
{
p_id = value;
}
}
public string FirstName
{
get
{
return first_name;
}
set
{
first_name = value;
}
}
public string MiddleName
{
get
{
return mid_name;
}
set
{
mid_name = value;
}
}
public string LastName
{
get
{
return last_name;
}
set
{
last_name = value;
}
}
public short Age
{
get
{
return p_age;
}
set
{
p_age = value;
}
}
public char? Sex
{
get
{
return p_sex;
}
set
{
p_sex = value;
}
}
}
}
Now go to the Program.cs or Module.vb and write the following code to add Person objects to the List(T) collection:
static void Main(string[] args)
{
ListpList = new List ();
pList.Add(new Person(1, "John", "", "Shields", 29, 'M'));
pList.Add(new Person(2, "Mary", "Matthew", "Jacobs", 35, 'F'));
pList.Add(new Person(3, "Amber", "Carl", "Agar", 25, 'M'));
pList.Add(new Person(4, "Kathy", "", "Berry", 21, 'F'));
pList.Add(new Person(5, "Lena", "Ashco", "Bilton", 33, 'F'));
pList.Add(new Person(6, "Susanne", "", "Buck", 45, 'F'));
pList.Add(new Person(7, "Jim", "", "Brown", 38, 'M'));
pList.Add(new Person(8, "Jane", "G", "Hooks", 32, 'F'));
pList.Add(new Person(9, "Robert", "", "", 31, 'M'));
pList.Add(new Person(10, "Cindy", "Preston", "Fox", 25, 'F'));
pList.Add(new Person(11, "Gina", "", "Austin", 27, 'F'));
pList.Add(new Person(12, "Joel", "David", "Benson", 33, 'M'));
pList.Add(new Person(13, "George", "R", "Douglas", 55, 'M'));
pList.Add(new Person(14, "Richard", "", "Banks", 22, 'M'));
pList.Add(new Person(15, "Mary", "C", "Shaw", 39, 'F'));
}
I have also created a common method ‘PrintOnConsole’ that will help us print the List(T) on the console:
static void PrintOnConsole(ListpList, string info)
{
Console.WriteLine(info);
Console.WriteLine("\n{0,2} {1,7} {2,8} {3,8} {4,2} {5,3}",
"ID", "FName", "MName", "LName", "Age", "Sex");
pList.ForEach(delegate(Person per)
{
Console.WriteLine("{0,2} {1,7} {2,8} {3,8} {4,2} {5,3}",
per.ID, per.FirstName, per.MiddleName, per.LastName, per.Age, per.Sex);
});
Console.ReadLine();
}
1. Looping through all items in the List(T)
PrintOnConsole(pList, "1. --- Looping through all items in the List---");
2. Filtering List(T) using a single condition - (Age > 35)
ListfilterOne = pList.FindAll(delegate(Person p) { return p.Age > 35; });
PrintOnConsole(filterOne, "2. --- Filtering Liston single condition (Age > 35) ---");
3. Filtering List(T) on multiple conditions (Age > 35 and Sex is Female)
ListfilterMultiple = pList.FindAll(delegate(Person p) { return p.Age > 35 && p.Sex == 'F'; });
PrintOnConsole(filterMultiple, "3. --- Filtering Liston multiple conditions (Age > 35 and Sex is Female) ---");
4. Sorting List(T) (Sort on FirstName)
ListsortFName = pList;
sortFName.Sort(delegate(Person p1, Person p2)
{
return p1.FirstName.CompareTo(p2.FirstName);
});
PrintOnConsole(sortFName, "4. --- Sort List(Sort on FirstName) ---");
<
5. Sorting List(T) descending (Sort on LastName descending)
ListsortLNameDesc = pList;
sortLNameDesc.Sort(delegate(Person p1, Person p2)
{
return p2.LastName.CompareTo(p1.LastName);
});
PrintOnConsole(sortLNameDesc, "5. --- Sort Listdescending (Sort on LastName descending) ---");
6. Add new List(T) to existing List(T)
ListnewList = new List ();
newList.Add(new Person(16, "Geoff", "", "Fisher", 29, 'M'));
newList.Add(new Person(17, "Samantha", "Carl", "Baxer", 32, 'F'));
pList.AddRange(newList);
PrintOnConsole(pList, "6. --- Add new Listto existing List<> ---");
7. Remove multiple items from List(T) based on condition (remove male employees)
ListremoveList = pList;
removeList.RemoveAll(delegate(Person p) { return p.Sex == 'M'; });
PrintOnConsole(removeList, "7. --- Remove multiple items from List<> based on condition ---");
8. Create Read Only List(T)
Console.WriteLine("8. --- Create Read Only List<> ---");
IList personReadOnly = pList;
Console.WriteLine("Before - Is List Read Only? True or False : " + personReadOnly.IsReadOnly);
personReadOnly = pList.AsReadOnly();
Console.WriteLine("After - Is List Read Only? True or False : " + personReadOnly.IsReadOnly);
Console.ReadLine();
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