beginner⏱35 minutesLesson 6 of 9

Data Structures: Arrays and Objects

Learn to organize data using arrays and objects

Data Structures: Arrays and Objects

Individual variables are not enough when you need to work with collections of data. Arrays and objects let you organize related values together.

Arrays

An array is an ordered list of values:

javascript

let colors = ["red", "green", "blue"];
let numbers = [10, 20, 30, 40];
let mixed = ["text", 42, true, null];

Accessing Elements

Elements are accessed by their index, starting at 0:

javascript

let fruits = ["Apple", "Banana", "Cherry"];

console.log(fruits[0]);  // Output: Apple
console.log(fruits[1]);  // Output: Banana
console.log(fruits[2]);  // Output: Cherry

Modifying Arrays

javascript

fruits[1] = "Blueberry";  // Replace "Banana"
console.log(fruits);       // ["Apple", "Blueberry", "Cherry"]

fruits.push("Date");       // Add to the end
fruits.pop();              // Remove from the end
fruits.unshift("Apricot"); // Add to the front
fruits.shift();            // Remove from the front

Array Properties and Methods

javascript

let items = [3, 1, 4, 1, 5];

console.log(items.length);     // Output: 5
console.log(items.indexOf(4)); // Output: 2
items.sort();
console.log(items);            // [1, 1, 3, 4, 5]

Objects

Objects store key-value pairs:

javascript

let person = {
  name: "Alice",
  age: 30,
  isStudent: false
};

Accessing and Modifying Properties

javascript

// Dot notation
console.log(person.name);   // Output: Alice
person.age = 31;

// Bracket notation (useful for dynamic keys)
console.log(person["name"]); // Output: Alice
person["isStudent"] = true;

// Adding new properties
person.city = "New York";

ℹ️Note

Use dot notation when you know the key name. Use bracket notation when the key comes from a variable.

Nested Structures

Objects and arrays can contain each other:

javascript

let classroom = {
  teacher: "Mr. Smith",
  students: [
    { name: "Alice", grade: 85 },
    { name: "Bob", grade: 92 },
    { name: "Charlie", grade: 78 }
  ],
  subject: "Programming"
};

console.log(classroom.students[0].name);  // Output: Alice
console.log(classroom.students[1].grade); // Output: 92

Iterating Over Objects

javascript

let car = { make: "Toyota", model: "Corolla", year: 2023 };

for (let key in car) {
  console.log(key + ":", car[key]);
}
// Output:
// make: Toyota
// model: Corolla
// year: 2023

Practice Exercise

Create a program that manages a simple library of books:

javascript

let library = [
  { title: "1984", author: "George Orwell", year: 1949 },
  { title: "To Kill a Mockingbird", author: "Harper Lee", year: 1960 }
];

function addBook(title, author, year) {
  library.push({ title, author, year });
}

function findBooksByAuthor(author) {
  return library.filter(book => book.author === author);
}

addBook("The Great Gatsby", "F. Scott Fitzgerald", 1925);
console.log(library.length);  // Output: 3

Summary

Structure	Use	Example
Array `[]`	Ordered list	`["a", "b", "c"]`
Object `{}`	Key-value pairs	`{ name: "Alice", age: 30 }`
Array of objects	List of structured data	`[{ id: 1 }, { id: 2 }]`

Next Steps

With variables, functions, control flow, and data structures under your belt, the next lesson explores a different paradigm: functional programming with Python.

Progress67%

Control Flow: Repeating with Loops

Introduction to Functional Programming with Python

Course Content

1. Getting Started with Programming 2. Understanding Variables 3. Functions: Reusable Code Blocks 4. Control Flow: Making Decisions with Conditionals 5. Control Flow: Repeating with Loops 6. Data Structures: Arrays and Objects 7. Introduction to Functional Programming with Python 8. Compiled Programming Languages with Rust 9. Declarative Programming: SQL and HCL