List in C# is a Generic collection type that allows to access its items by index, List<T> represents a list of strongly typed objects, where T is the data type. List has properties similar to an Array, however it expands automatically as the number of elements increases.
If you haven’t gone through my blog on Generics in C#, then please do it here.
Create a List in C# :
You need to specify a type parameter T while creating a List<T>. lets look at below example.
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//Creating a list of string objects List<string> lstCountry = new List<string>(); //Creating a list of int objects var lstNumbers = new List<int>(); |
In above example.
- List<string> lstCountry = new List<string>(); It creates a list that holds only string values.
- var lstNumbers = new List<int>(); It creates a list that holds only int values.
Add item to a List in C# :
You can use Add() method to add new item to a List<T> of same type.
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//Creating a list of string objects List<string> lstCountry = new List<string>(); //Adding items to lstCountry list object lstCountry.Add("India"); lstCountry.Add("United States"); lstCountry.Add("United Kingdom"); lstCountry.Add("Spain"); //Creating a list of int objects var lstNumbers= new List<int>(); //Adding items to lstNumbers list object lstNumbers.Add(11); lstNumbers.Add(12); lstNumbers.Add(13); lstNumbers.Add(14); |
In above, we are adding string items to list lstCountry and int values to list lstNumbers using Add() method.
Create a List using object initializer syntax :
While using object initializer syntax , we can also create a strongly typed list of object and add elements to it in a single statement.
In below example, we are creating a list using object initializer syntax.
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//Declaring a collection object and adding items using //collection-initializer syntax List<string> lstCountry = new List<string>() { "India", "United States", "United Kingdom", "Spain" }; //Using var keyword var lstNumbers = new List<int>() { 11, 12, 13, 14, 15, 16 }; |
Add list of Items in to another List in C# :
You can use the AddRange(IEnumerable<T> collection) method to add list of items or an array of items in to another List<T>, lets have a look at below example.
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//Creating a list of string objects List<string> lstCountry = new List<string>(); //Adding items to lstCountry object lstCountry.Add("India"); lstCountry.Add("United States"); lstCountry.Add("United Kingdom"); lstCountry.Add("Spain"); //Adding another list of items using AddRange method lstCountry.AddRange(new List<string>() { "Poland", "Greece", "Germany" }); //Adding an array of item to the list lstCountry.AddRange(new string[] { "Italy", "Brazil", "Peru", "Canada" }); |
Here in above,
- lstCountry.AddRange(new List<string>() { "Poland", "Greece", "Germany" }); adds a new list of string items to lstCountry.
- lstCountry.AddRange(new string[] { "Italy", "Brazil", "Peru", "Canada" }); adds an array of string items to lstCountry.
Remove an item from a List in C# :
We have various methods available to remove an item from a List<T>.
- bool Remove(T item) : This method removes first occurrence of the specified element.
- void RemoveAt(int index) : This method removes an element from the specified index.
- void RemoveRange(int index, int count) : This method removes a range of elements from the List, here index value is the starting point and count is the number of items to be removed.
Lets have a look at below example.
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//Creating a list of string objects List<string> lstCountry = new List<string>(); //Adding items to lstCountry object lstCountry.Add("India"); lstCountry.Add("United States"); lstCountry.Add("United Kingdom"); lstCountry.Add("Spain"); //Remove first occurrence of item - it will remove "United States" from the list lstCountry.Remove("United States"); //Or //Remove item at 1st index, index starts from 0 lstCountry.RemoveAt(1); |
In above, the statement lstCountry.RemoveAt(1); removes “United States” , which is at index 1 from the list.
We can also use Remove() method to remove a specific item from the list, for example lstCountry.Remove("United States");
We can use RemoveRange() to remove a range of items from the list. lets have a look at below example.
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//Creating a list of string objects List<string> lstCountry = new List<string>(); //Adding items to lstCountry object lstCountry.Add("India"); lstCountry.Add("United States"); lstCountry.Add("United Kingdom"); lstCountry.Add("Spain"); //Removes a range of elements //This will remove "India" and "United States" from the list lstCountry.RemoveRange(0, 2); |
In above example, we have used start index as 0 and number of elements removed as 2 , which removes “India” and “United States” from the list.
Read items in a List in C# :
We can access or read elements in List using the index operator and for-each loop.
Lets have a look at below example.
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//Creating a list of string objects List<string> lstCountry = new List<string>(); //Adding items to lstCountry object lstCountry.Add("India"); lstCountry.Add("United States"); lstCountry.Add("United Kingdom"); lstCountry.Add("Spain"); //Using foreach loop, we can traverse through a list and access each item Console.WriteLine("Read items in List using ForEach loop"); Console.WriteLine("**************************************"); foreach (string country in lstCountry) Console.WriteLine(country); Console.WriteLine("Read items in List using For loop and index value"); Console.WriteLine("**************************************"); for (int i = 0; i < lstCountry.Count; i++) Console.WriteLine(lstCountry[i]); |
Find the output as below :
Example :
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using System; using System.Collections.Generic; namespace ListCollectionExample { class Program { static void Main(string[] args) { //Creating a list of string objects List<string> lstCountry = new List<string>(); //Adding items to lstCountry object lstCountry.Add("India"); lstCountry.Add("United States"); lstCountry.Add("United Kingdom"); lstCountry.Add("Spain"); //Using foreach loop, we can travers through a list and access each item Console.WriteLine("Items in the List"); Console.WriteLine("**************************************"); foreach (string country in lstCountry) Console.WriteLine(country); Console.WriteLine("**************************************"); //Adding another list of items using AddRange method lstCountry.AddRange(new List<string>() { "Poland", "Greece", "Germany" }); //Adding a range of items Console.WriteLine("After Adding new range of list items \"Poland\",\"Greece\",\"Germany\""); Console.WriteLine("Items in the List"); Console.WriteLine("**************************************"); foreach (string country in lstCountry) Console.WriteLine(country); Console.WriteLine("**************************************"); //Adding an array of item to the list lstCountry.AddRange(new string[] { "Italy", "Brazil", "Peru", "Canada" }); Console.WriteLine("After Adding new range of aray of items \"Italy\",\"Brazil\",\"Peru\", \"Canada\""); Console.WriteLine("Items in the List"); Console.WriteLine("**************************************"); foreach (string country in lstCountry) Console.WriteLine(country); Console.WriteLine("**************************************"); //Removes a range of elements //This will remove "India" and "United States" from the list lstCountry.RemoveRange(0, 2); Console.WriteLine("After Removing \"India\" and \"United States\" from the list"); Console.WriteLine("Items in the List"); Console.WriteLine("**************************************"); foreach (string country in lstCountry) Console.WriteLine(country); } } } |
Find the output as below :
Important methods and properties of List<T> type in C# :
List<T>.Count : It is a property , that is used to get the number of elements present in a List<T>.
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//Creating a list of integer objects var lstNumbers = new List<int>() { 11, 12, 13, 14, 15, 16 }; //Get the total element count Console.WriteLine("Total Number Of Element : {0}" , lstNumbers.Count); //Prints Total Number Of Element : 6 |
List<T>.Clear() : this method used to remove all from a List<T>.
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//Creating a list of integer objects var lstNumbers = new List<int>() { 11, 12, 13, 14, 15, 16 }; //Removes all elements from the list lstNumbers.Clear(); //We have removed all elements using Clear() function //Hence it prints Total Number Of Element : 0 Console.WriteLine("Total Number Of Element : {0}" , lstNumbers.Count); |
List<T>.Contains() : This method checks whether a specified item exists or not in a List<T>, it returns true if item exists or else returns false.
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//Creating a list of integer objects var lstNumbers = new List<int>() { 11, 12, 13, 14, 15, 16 }; bool isExist15 = lstNumbers.Contains(15);//Returns true bool isExist20 = lstNumbers.Contains(20);//Returns false |
List<T>.Insert() : Inserts an element at the specified index in a List<T>. It takes an index and value to insert.
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//Creating a list of integer objects var lstNumbers = new List<int>() { 11, 12, 13, 14, 15, 16 }; //Inserts 20 at 2nd index: after 12. lstNumbers.Insert(2, 20); |
List<T>.Find() : It is a method, that finds first and single element based on the specified predicate function or a condition.
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//Creating a list of integer objects var lstNumbers = new List<int>() { 11, 12, 13, 14, 15, 16 }; //This will return 13, since it is the first element in the list that is > 12 var item = lstNumbers.Find(x => x > 12); |
There are couple of other methods that are basically used for sorting and searching a List<T> , We will cover that in next article.
Thanks for your time, feel free to provide your feedback and do check my other blogs on Generics and Var Type in C#.