C# List Methods

This repository provides an overview of commonly used methods for the List<T> class in C#. We'll focus on methods that can be called directly on a List<T> object, including both instance methods and extension methods.

Table of Contents

• Creating a List
• Add
• AddRange
• BinarySearch
• Clear
• Contains
• CopyTo
• EnsureCapacity
• TrimExcess
• Equals
• Exists, Find, FindAll
• FindIndex, FindLast, FindLastIndex
• ForEach
• GetRange
• IndexOf and LastIndexOf
• Insert and InsertRange
• Remove, RemoveAt, RemoveRange
• RemoveAll
• Reverse
• Sort
• ToArray
• Object Methods

Creating a List

Let's start with a simple List<int> that we'll use for our examples:

List<int> numbers = new List<int>() { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };

Add ⭐

The Add method is used to add an item to the end of the list.

numbers.Add(11);
// numbers is now { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 }

AddRange ⭐

AddRange takes a collection and adds all its elements to the end of the list.

numbers.AddRange(new int[] { 12, 13, 14 });
// numbers is now { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 }

BinarySearch

BinarySearch searches a sorted list for a specific element and returns the index of the element if found.

List<int> sortedNumbers = new List<int>() { 2, 4, 6, 8, 10, 12, 14, 16, 18, 20 };
int index = sortedNumbers.BinarySearch(12);
Console.WriteLine($"Index of 12: {index}"); // Output: Index of 12: 5

Clear ⭐

The Clear method removes all elements from the list.

numbers.Clear();
Console.WriteLine($"Count: {numbers.Count}, Capacity: {numbers.Capacity}");
// Output: Count: 0, Capacity: 16

Contains ⭐

Contains checks if an item is in the list and returns a boolean.

bool hasThree = numbers.Contains(3);
Console.WriteLine($"List contains 3: {hasThree}");

CopyTo

CopyTo copies elements from the list to an array. It has several overloads:

int[] array = new int[numbers.Count];
numbers.CopyTo(array);
// array now contains all elements from numbers

EnsureCapacity

EnsureCapacity ensures that the list has at least the specified capacity.

numbers.EnsureCapacity(20);
Console.WriteLine($"Capacity after EnsureCapacity(20): {numbers.Capacity}");
// Output: Capacity after EnsureCapacity(20): 32 (doubles the previous capacity of 16)

TrimExcess

TrimExcess trims the excess capacity to minimize the memory footprint.

numbers.TrimExcess();
Console.WriteLine($"Capacity after TrimExcess: {numbers.Capacity}");
// Output will depend on the current count of the list

Equals

Equals compares two list addresses unless overridden.

List<int> numbers2 = new List<int>() { 1, 2, 3, 4, 5 };
bool areEqual = numbers.Equals(numbers2);
Console.WriteLine($"Lists are equal: {areEqual}");
// Output: Lists are equal: False (comparing references, not contents)

Exists, Find, FindAll ⭐

These methods use delegates (predicates) to search the list:

bool hasMultipleOfThree = numbers.Exists(n => n % 3 == 0);
// Returns true if any number is divisible by 3

int firstMultipleOfThree = numbers.Find(n => n % 3 == 0);
// Returns the first number divisible by 3

List<int> allMultiplesOfThree = numbers.FindAll(n => n % 3 == 0);
// Returns a new list with all numbers divisible by 3

FindIndex, FindLast, FindLastIndex

These methods find the index of elements that match a predicate:

int indexOfFirstEven = numbers.FindIndex(n => n % 2 == 0);
// Returns the index of the first even number

int lastEven = numbers.FindLast(n => n % 2 == 0);
// Returns the last even number

int indexOfLastEven = numbers.FindLastIndex(n => n % 2 == 0);
// Returns the index of the last even number

ForEach

ForEach performs an action on each element of the list:

numbers.ForEach(n => Console.Write(n + " "));
// Prints all numbers in the list

GetRange

GetRange returns a new list containing a specified range of elements:

List<int> subList = numbers.GetRange(2, 3);
// subList contains { 3, 4, 5 } (starting at index 2, taking 3 elements)

IndexOf and LastIndexOf

These methods find the index of a specific item:

int indexOfFive = numbers.IndexOf(5);
// Returns the index of the first occurrence of 5

int lastIndexOfFive = numbers.LastIndexOf(5);
// Returns the index of the last occurrence of 5

Insert and InsertRange

These methods insert elements at a specific position:

numbers.Insert(2, 100);
// Inserts 100 at index 2

numbers.InsertRange(3, new int[] { 101, 102 });
// Inserts 101 and 102 starting at index 3

Remove, RemoveAt, RemoveRange

These methods remove elements from the list:

numbers.Remove(5);
// Removes the first occurrence of 5

numbers.RemoveAt(0);
// Removes the element at index 0

numbers.RemoveRange(1, 3);
// Removes 3 elements starting at index 1

RemoveAll

RemoveAll removes all elements that match a predicate:

int removedCount = numbers.RemoveAll(x => x % 2 == 1);
Console.WriteLine($"Removed {removedCount} odd numbers");
// Removes all odd numbers from the list

Reverse

Reverse reverses the order of elements in the list:

numbers.Reverse();
// Reverses the order of all elements in the list

Sort

Sort sorts the elements in the list:

numbers.Sort();
// Sorts the list in ascending order

ToArray

ToArray creates an array from the list:

int[] arrayFromList = numbers.ToArray();
// Creates a new array containing all elements from the list

Object Methods

These are inherited from the Object class:

Type listType = numbers.GetType();
// Gets the Type of the list

bool isEqual = numbers.Equals(numbers2);
// Compares references (unless overridden)

string listString = numbers.ToString();
// Returns a string representation of the list

int hashCode = numbers.GetHashCode();
// Gets the hash code for the list

This README provides an overview of common List<T> methods in C#. Each method is accompanied by a brief explanation and example usage. The ⭐ symbol indicates methods that are most commonly used.

Remember to always refer to the official Microsoft documentation for the most up-to-date and comprehensive information on List<T> methods.