Зміст курсу
C# Beyond Basics
C# Beyond Basics
List Methods
In the previous chapter we learnt how to declare, initialize and add elements to a list. Additionally we also looked at how we would access elements of a list and loop through them. In this chapter we will look at some useful list methods.
1. Remove()
The Remove method removes the first instance of an element from a list.
Syntax: exampleList.remove(targetElement);
index.cs
using System; using System.Collections.Generic; namespace ConsoleApp { class Program { static void Main(string[] args) { List<string> fruits = new List<string> { "Apple", "Banana", "Orange", "Banana", "Grape" }; Console.Write("Before: "); foreach (string fruit in fruits) { Console.Write(fruit + " "); } fruits.Remove("Banana"); Console.Write("\nAfter: "); foreach (string fruit in fruits) { Console.Write(fruit + " "); } } } }
In case no such element is found, it simply doesn't do anything:
index.cs
using System; using System.Collections.Generic; namespace ConsoleApp { class Program { static void Main(string[] args) { List<string> fruits = new List<string> { "Apple", "Banana", "Orange", "Banana", "Grape" }; Console.Write("Before: "); foreach (string fruit in fruits) { Console.Write(fruit + " "); } fruits.Remove("some element"); // trying to remove an unknown element Console.Write("\nAfter: "); foreach (string fruit in fruits) { Console.Write(fruit + " "); } } } }
2. RemoteAt()
The RemoveAt method removes an element at a specific index.
Syntax: exampleList.RemoveAt(index);
index.cs
using System; using System.Collections.Generic; namespace ConsoleApp { class Program { static void Main(string[] args) { List<string> fruits = new List<string> { "Apple", "Orange", "Banana", "Grape" }; Console.Write("Before: "); foreach (string fruit in fruits) { Console.Write(fruit + " "); } fruits.RemoveAt(1); Console.Write("\nAfter: "); foreach (string fruit in fruits) { Console.Write(fruit + " "); } } } }
3. Clear
The Clear method simply removes all elements from a list. It takes no arguments.
Syntax: exampleList.Clear();
index.cs
using System; using System.Collections.Generic; namespace ConsoleApp { class Program { static void Main(string[] args) { List<string> fruits = new List<string> { "Apple", "Orange", "Banana", "Grape" }; Console.Write("Before: "); foreach (string fruit in fruits) { Console.Write(fruit + " "); } fruits.Clear(); Console.Write("\nAfter: "); foreach (string fruit in fruits) { Console.Write(fruit + " "); } } } }
4. Insert
The Insert method inserts an element in the list at a specified index.
Syntax: exampleList.Insert(index, elementToInsert);
index.cs
using System; using System.Collections.Generic; namespace ConsoleApp { class Program { static void Main(string[] args) { List<int> numbers = new List<int> { 2, 4, 6, 10, 12 }; Console.Write("Before: "); foreach (int number in numbers) Console.Write(number + " "); numbers.Insert(3, 8); Console.Write("\nAfter: "); foreach (int number in numbers) Console.Write(number + " "); } } }
We can omit the curly braces {} in case there's only a single statement inside an if-condition, a for-loop, or a foreach loop. For-example:
index.cs
foreach(int number in numbers) { Console.Write(number + " "); }
The above snippet is the same as:
index.cs
foreach(int number in numbers) Console.Write(number + " ");
If there's already an element at the specified index, it is pushed to the right, and so are the remaining elements of the array after it - in case there are any. The following diagram illustrates the process:
5. Contains()
The Contains method checks if a list contains a specific element. It returns a boolean value (true or false).
Syntax: exampleList.Contains(element);
index.cs
using System; using System.Collections.Generic; namespace ConsoleApp { class Program { static void Main(string[] args) { List<char> vowels = new List<char> { 'a', 'e', 'i', 'o', 'u' }; Console.WriteLine("Contains 'o': " + vowels.Contains('o')); } } }
6. IndexOf()
The IndexOf method returns the index of the first occurrence of an element in a list.
Syntax: exampleList.IndexOf(element);
index.cs
using System; using System.Collections.Generic; namespace ConsoleApp { class Program { static void Main(string[] args) { List<char> vowels = new List<char> { 'a', 'e', 'i', 'o', 'u' }; vowels.Remove('o'); Console.WriteLine("Index of 'o': " + vowels.IndexOf('o')); } } }
If the element doesn't exist in the list, it simply returns -1:
The indexOf method is especially useful when we want to access an element by index but we won't know it's index. For-example in the vowels, we want to access the element o by index and change it to capital O:
index.cs
using System; using System.Collections.Generic; namespace ConsoleApp { class Program { static void Main(string[] args) { List<char> vowels = new List<char> { 'a', 'e', 'i', 'o', 'u' }; int targetIndex = vowels.IndexOf('o'); Console.WriteLine(vowels[targetIndex]); vowels[targetIndex] = 'O'; Console.WriteLine(vowels[targetIndex]); } } }
1. What does the Remove() method do?
2. What is the fastest way of checking if a list contains a specific element?
3. Which method is used for removing all elements from a list?
4. What will be the output of the following code?
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