Iterating Over Collections
Use each, map, select, and other iteration methods to process collections effectively.
Iterating Over Collections is a free Ruby Academy lesson on CoddyKit — lesson 2 of 3. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Ruby Academy learning path, one of 3 lessons in the course, and your progress syncs across the web and the CoddyKit app.
1
Iterating Over Collections
Iteration allows you to process each element in an array or hash.
In this lesson, you will learn how to use methods like each, map, and select.
2
Using Each with Arrays
The each method loops through each element in an array.
[1, 2, 3].each { |num| puts num * 2 }3
Using Each with Hashes
The each method can be used to loop through key-value pairs.
{ 'name' => 'Alice', 'age' => 25 }.each { |key, value| puts "#{key}: #{value}" }4
Using Map
The map method transforms each element in an array and returns a new array.
numbers = [1, 2, 3]
squared = numbers.map { |n| n * n }
puts squared5
Using Select
The select method filters elements based on a condition.
numbers = [1, 2, 3, 4, 5]
even_numbers = numbers.select { |n| n.even? }
puts even_numbers6
Using Reject
The reject method excludes elements that match a condition.
numbers = [1, 2, 3, 4, 5]
odd_numbers = numbers.reject { |n| n.even? }
puts odd_numbers7
Using Reduce
The reduce method accumulates values in an array.
sum = [1, 2, 3, 4, 5].reduce(0) { |acc, num| acc + num }
puts sum8
9
Alternative Ways to Iterate
You can also use times and upto for loops.
5.times { |i| puts "Iteration #{i+1}" }
1.upto(3) { |n| puts "Number: #{n}" }10
Congratulations!
You have learned how to iterate over collections using various methods.
Next, you will explore useful array and hash methods.
Frequently asked questions
Is the “Iterating Over Collections” lesson free?
Yes — the full text of “Iterating Over Collections” is free to read here on the web, and the Ruby Academy course includes 3 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Ruby Academy course, upgrade to CoddyKit PRO.
What will I learn in “Iterating Over Collections”?
Use each, map, select, and other iteration methods to process collections effectively. You practise Ruby Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Ruby Academy?
No prior experience is required. Ruby Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 2 of 3, so you can start here or from the beginning and move at your own pace.
How long does the “Iterating Over Collections” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Ruby Academy lesson?
Yes. Every Ruby Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- Arrays and Hashes
- Iterating Over Collections
- Useful Array and Hash Methods