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Ruby Academy · Lesson

Iterating Over Collections

Use each, map, select, and other iteration methods to process collections effectively.

Lesson 2 of 310 steps

Iterating Over Collections is a free Ruby Academy lesson on CoddyKit. This is lesson 2 of 3. Any 3 lessons of this learning path are free to read in full — after that, CoddyKit PRO unlocks every lesson, plus hands-on practice with a built-in code editor and a 24/7 AI tutor. It is part of the Ruby Academy learning path, and your progress syncs across the web and the CoddyKit app. The Ruby Academy course includes 3 lessons in total.

Introduction to Iteration

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.

Iterating Over Collections — illustration 1

Using Each with Arrays

The each method loops through each element in an array.

[1, 2, 3].each { |num| puts num * 2 }

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}" }

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 squared

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_numbers

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_numbers

Using Reduce

The reduce method accumulates values in an array.

sum = [1, 2, 3, 4, 5].reduce(0) { |acc, num| acc + num }
puts sum

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}" }

Congratulations!

You have learned how to iterate over collections using various methods.

Next, you will explore useful array and hash methods.

Iterating Over Collections — illustration 10
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Frequently Asked Questions

Is the “Iterating Over Collections” lesson free?

Yes — any 3 lessons of the Ruby Academy learning path, including “Iterating Over Collections”, are free to read in full here on the web. After that, CoddyKit PRO unlocks every lesson, plus interactive practice with a built-in code editor and a 24/7 AI tutor. The Ruby Academy course includes 3 lessons in total.

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, so you can start here or from the beginning and move at your own pace. This is lesson 2 of 3.

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

  1. Arrays and Hashes
  2. Iterating Over Collections
  3. Useful Array and Hash Methods
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