Modifying Arrays

Part of the Fundamentals section of Coddy's Swift journey — lesson 64 of 86.

Arrays become truly useful when you can change their contents. To modify an array, you must declare it with var instead of let.

You can change an existing element by assigning a new value to a specific index:

var colors = ["Red", "Green", "Blue"]
colors[1] = "Yellow"
print(colors)  // ["Red", "Yellow", "Blue"]

To add new elements, use the append method for a single item, or the += operator to add multiple items at once:

var numbers = [1, 2, 3]
numbers.append(4)
print(numbers)  // [1, 2, 3, 4]

numbers += [5, 6]
print(numbers)  // [1, 2, 3, 4, 5, 6]

To insert an element at a specific position, use the insert method:

var fruits = ["Apple", "Orange"]
fruits.insert("Banana", at: 1)
print(fruits)  // ["Apple", "Banana", "Orange"]

To remove elements, use remove(at:) with the index you want to delete:

var items = ["A", "B", "C", "D"]
items.remove(at: 2)
print(items)  // ["A", "B", "D"]

Remember, when you remove an element, all subsequent elements shift down to fill the gap.

Challenge

Easy

Write a function modifyInventory that takes an array of items, a new item to add, and an index to remove, then returns the modified array.

Perform the following operations in order:

Change the first element to "Updated"
Append the new item to the end of the array
Remove the element at the specified index

Parameters:

items ([String]): The initial array of items
newItem (String): The item to append
removeIndex (Int): The index of the element to remove (after appending)

Returns: The modified array after all operations ([String])

Example: If items is ["A", "B", "C"], newItem is "D", and removeIndex is 2, the function should:

Change first element: ["Updated", "B", "C"]
Append "D": ["Updated", "B", "C", "D"]
Remove at index 2: ["Updated", "B", "D"]

Cheat sheet

Arrays declared with var can be modified, while arrays declared with let are immutable.

Change an element by assigning a new value to a specific index:

var colors = ["Red", "Green", "Blue"]
colors[1] = "Yellow"  // ["Red", "Yellow", "Blue"]

Add a single element with append:

var numbers = [1, 2, 3]
numbers.append(4)  // [1, 2, 3, 4]

Add multiple elements with +=:

numbers += [5, 6]  // [1, 2, 3, 4, 5, 6]

Insert an element at a specific position with insert(_:at:):

var fruits = ["Apple", "Orange"]
fruits.insert("Banana", at: 1)  // ["Apple", "Banana", "Orange"]

Remove an element at a specific index with remove(at:):

var items = ["A", "B", "C", "D"]
items.remove(at: 2)  // ["A", "B", "D"]

When an element is removed, all subsequent elements shift down to fill the gap.

Try it yourself

func modifyInventory(items: [String], newItem: String, removeIndex: Int) -> [String] {
    // Write code here
}

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

All lessons in Fundamentals

1Introduction

The Language Hello World!Comments

4Operators Part 1

Arithmetic Operators Modulo Operator Compound Assignment Recap - Simple Math Comparison Operators

7Basic IO

Print Function String Interpolation ReadLine Input Type Conversion Recap - Till 120 Recap - True or False

10Functions

Declare A Function Parameters And Arguments Return Values Argument Labels Recap - Sigma Function Recap - Validation Function Default Values

13Iterating Over Sequences

Iterating Over Elements The Enumerated Method Iterating Over Strings P1 Iterating Over Strings P2

16Final Challenges

Flat Asterisk Pyramid Pattern Finder What To Buy

2Variables

Let vs Var Type Annotations Numbers String Boolean Naming Conventions Recap - Initialize Variables

5Operators Part 2

Logical Operators Part 1 Logical Operators Part 2 Recap - Simple Logic Logical Operators Part 3 Ternary Operator

8Bill Split Calculator

Welcome Message Getting Input

Calculating Tip And Total

Splitting The Bill

Formatted Output

11FizzBuzz with a Twist

Game Overview The FizzBuzz Function

Looping The Numbers

Adding The Twist

14Arrays Advanced

Array Slicing Part 1 Array Slicing Part 2 Sequence Operators The Contains Method