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Collection vs List C#

C# - List

The List is a collection of strongly typed objects that can be accessed by index and having methods for sorting, searching, and modifying list. It is the generic version of the ArrayList that comes under System.Collection.Generic namespace.

List Characteristics

List equivalent of the ArrayList, which implements IList.
It comes under System.Collections.Generic namespace.
List can contain elements of the specified type. It provides compile-time type checking and doesn't perform boxing-unboxing because it is generic.
Elements can be added using the Add[], AddRange[] methods or collection-initializer syntax.
Elements can be accessed by passing an index e.g. myList[0]. Indexes start from zero.
List performs faster and less error-prone than the ArrayList.

Creating a List

The List is a generic collection, so you need to specify a type parameter for the type of data it can store. The following example shows how to create list and add elements.

Example: Adding elements in List

List primeNumbers = new List[]; primeNumbers.Add[1]; // adding elements using add[] method primeNumbers.Add[3]; primeNumbers.Add[5]; primeNumbers.Add[7]; var cities = new List[]; cities.Add["New York"]; cities.Add["London"]; cities.Add["Mumbai"]; cities.Add["Chicago"]; cities.Add[null];// nulls are allowed for reference type list //adding elements using collection-initializer syntax var bigCities = new List[] { "New York", "London", "Mumbai", "Chicago" };

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In the above example, List primeNumbers = new List[]; creates a list of int type. In the same way, cities and bigCities are string type list. You can then add elements in a list using the Add[] method or the collection-initializer syntax.

You can also add elements of the custom classes using the collection-initializer syntax. The following adds objects of the Student class in the List.

Example: Add Custom Class Objects in List

var students = new List[] { new Student[]{ Id = 1, Name="Bill"}, new Student[]{ Id = 2, Name="Steve"}, new Student[]{ Id = 3, Name="Ram"}, new Student[]{ Id = 4, Name="Abdul"} };

Adding an Array in a List

Use the AddRange[] method to add all the elements from an array or another collection to List.

AddRange[] signature: void AddRange[IEnumerable collection]

Example: Add Arrays in List

string[] cities = new string[3]{ "Mumbai", "London", "New York" }; var popularCities = new List[]; // adding an array in a List popularCities.AddRange[cities]; var favouriteCities = new List[]; // adding a List favouriteCities.AddRange[popularCities];

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Accessing a List

A list can be accessed by an index, a for/foreach loop, and using LINQ queries. Indexes of a list start from zero. Pass an index in the square brackets to access individual list items, same as array. Use a foreach or for loop to iterate a List collection.

Example: Accessing List

List numbers = new List[] { 1, 2, 5, 7, 8, 10 }; Console.WriteLine[numbers[0]]; // prints 1 Console.WriteLine[numbers[1]]; // prints 2 Console.WriteLine[numbers[2]]; // prints 5 Console.WriteLine[numbers[3]]; // prints 7 // using foreach LINQ method numbers.ForEach[num => Console.WriteLine[num + ", "]];//prints 1, 2, 5, 7, 8, 10, // using for loop for[int i = 0; i < numbers.Count; i++] Console.WriteLine[numbers[i]];

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Accessing a List using LINQ

The List implements the IEnumerable interface. So, we can query a list using LINQ query syntax or method syntax, as shown below.

Example: LINQ Query on List

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Insert Elements in List

Use the Insert[] method inserts an element into the List collection at the specified index.

Insert[] signature:void Insert[int index, T item];

Example: Insert elements into List

var numbers = new List[]{ 10, 20, 30, 40 }; numbers.Insert[1, 11];// inserts 11 at 1st index: after 10. foreach [var num in numbers] Console.Write[num];

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Remove Elements from List

Use the Remove[] method to remove the first occurrence of the specified element in the List collection. Use the RemoveAt[] method to remove an element from the specified index. If no element at the specified index, then the ArgumentOutOfRangeException will be thrown.

Remove[] signature:bool Remove[T item]

RemoveAt[] signature: void RemoveAt[int index]

Example: Remove elements from List

var numbers = new List[]{ 10, 20, 30, 40, 10 }; numbers.Remove[10]; // removes the first 10 from a list numbers.RemoveAt[2]; //removes the 3rd element [index starts from 0] //numbers.RemoveAt[10]; //throws ArgumentOutOfRangeException foreach [var el in intList] Console.Write[el]; //prints 20 30

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Check Elements in List

Use the Contains[] method to determine whether an element is in the List or not.

Example: Contains[]

var numbers = new List[]{ 10, 20, 30, 40 }; numbers.Contains[10]; // returns true numbers.Contains[11]; // returns false numbers.Contains[20]; // returns true

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List Class Hierarchy

The following diagram illustrates the List hierarchy.

List Class Properties and Methods

The following table lists the important properties and methods of List class:

PropertyUsage

Items	Gets or sets the element at the specified index
Count	Returns the total number of elements exists in the List

MethodUsage

Add	Adds an element at the end of a List.
AddRange	Adds elements of the specified collection at the end of a List.
BinarySearch	Search the element and returns an index of the element.
Clear	Removes all the elements from a List.
Contains	Checks whether the specified element exists or not in a List.
Find	Finds the first element based on the specified predicate function.
Foreach	Iterates through a List.
Insert	Inserts an element at the specified index in a List.
InsertRange	Inserts elements of another collection at the specified index.
Remove	Removes the first occurrence of the specified element.
RemoveAt	Removes the element at the specified index.
RemoveRange	Removes all the elements that match the supplied predicate function.
Sort	Sorts all the elements.
TrimExcess	Sets the capacity to the actual number of elements.
TrueForAll	Determines whether every element in theList matches the conditions defined by the specified predicate.

C# - List

List Characteristics

Creating a List

Adding an Array in a List

Accessing a List

Accessing a List using LINQ

Insert Elements in List

Remove Elements from List

Check Elements in List

List Class Hierarchy

List Class Properties and Methods

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