Each for iteration in Ruby

Introduction

You use 'each' to repeat a set of actions for every item in a list or collection. It helps you handle many items one by one easily.

When you want to print every name in a list of friends.

When you need to add a number to each item in a list of prices.

When you want to check each word in a sentence for a condition.

When you want to perform the same task on every element in an array.

Syntax

Ruby

collection.each do |item|
  # code to run for each item
end

The 'collection' can be an array, hash, or any list of items.

The 'item' inside the pipes | | is a temporary name for each element as you go through the list.

Examples

Prints each number in the array one by one.

Ruby

numbers = [1, 2, 3]
numbers.each do |num|
  puts num
end

Prints each fruit name in uppercase using a shorter block syntax.

Ruby

fruits = ['apple', 'banana', 'cherry']
fruits.each { |fruit| puts fruit.upcase }

Loops through a hash and prints each key with its value.

Ruby

hash = {a: 1, b: 2}
hash.each do |key, value|
  puts "#{key} is #{value}"
end

Sample Program

This program goes through each color in the list and prints a sentence saying you like that color.

Ruby

colors = ['red', 'green', 'blue']
colors.each do |color|
  puts "I like #{color}"
end

Important Notes

You can use 'each' with arrays, hashes, and other collections.

Inside the block, you can do anything with the current item, like change it or use it in calculations.

The 'each' method does not change the original collection unless you do it explicitly.

Summary

Use 'each' to repeat actions for every item in a list.

The block between 'do' and 'end' runs once per item.

It works with arrays, hashes, and other collections.

Practice

1. What does the each method do in Ruby when used with an array?

easy

A. It removes duplicate elements from the array.

B. It runs the given block once for every element in the array.

C. It sorts the array in ascending order.

D. It returns the length of the array.

Solution

1. Step 1: Understand the purpose of each

   The each method is used to loop over every element in a collection like an array.

2. Step 2: Identify what happens inside the block

   The block given to each runs once for each element, allowing actions on each item.

3. Final Answer:

   It runs the given block once for every element in the array. -> Option B

4. Quick Check:

   each repeats actions per item [OK]

Hint: Remember: each runs code for every item in the list [OK]

Common Mistakes:

• Confusing each with sorting or filtering methods
• Thinking each returns a new array
• Assuming each counts elements

2. Which of the following is the correct syntax to iterate over an array numbers using each in Ruby?

easy

A. numbers.each do num puts num end

B. each numbers do |num| puts num end

C. numbers.each { |num| puts num }

D. numbers.each(num) { puts num }

Solution

1. Step 1: Recognize correct each syntax

   The each method is called on the array, followed by a block with a parameter inside pipes.

2. Step 2: Check block format

   numbers.each { |num| puts num } uses curly braces with a block parameter |num| and a valid block body puts num.

3. Final Answer:

   numbers.each { |num| puts num } -> Option C

4. Quick Check:

   Correct block syntax = numbers.each { |num| puts num } [OK]

Hint: Use .each with {|var| ...} or do |var| ... end [OK]

Common Mistakes:

• Placing the variable outside the pipes
• Calling each without a block
• Using parentheses incorrectly with each

3. What will be the output of this Ruby code?

fruits = ['apple', 'banana', 'cherry']
fruits.each do |fruit|
  puts fruit.upcase
end

medium

A. APPLE
BANANA
CHERRY

B. apple
banana
cherry

C. APPLE BANANA CHERRY

D. ['APPLE', 'BANANA', 'CHERRY']

Solution

1. Step 1: Understand the each loop behavior

   The code loops over each fruit and prints the uppercase version using puts fruit.upcase.

2. Step 2: Determine output format

   puts prints each string on a new line, so each fruit name appears uppercase on its own line.

3. Final Answer:

   APPLE BANANA CHERRY -> Option A

4. Quick Check:

   each + puts prints each item on a new line [OK]

Hint: puts prints each item on a new line inside each [OK]

Common Mistakes:

• Expecting output on one line
• Confusing puts with print
• Not applying upcase method

4. Identify the error in this Ruby code snippet:

numbers = [1, 2, 3]
numbers.each do num
  puts num * 2
end

medium

A. Missing pipes around the block variable 'num'.

B. Incorrect method name; should be 'for' instead of 'each'.

C. Missing parentheses after 'each'.

D. Using 'puts' inside the block is not allowed.

Solution

1. Step 1: Check block variable syntax

   In Ruby, block variables must be enclosed in pipes like |num| when using do...end.

2. Step 2: Identify the missing pipes

   The code uses do num instead of do |num|, causing a syntax error.

3. Final Answer:

   Missing pipes around the block variable 'num'. -> Option A

4. Quick Check:

   Block variables need pipes |var| [OK]

Hint: Always put block variables inside |pipes| with do...end [OK]

Common Mistakes:

• Omitting pipes around block variables
• Thinking parentheses are required after each
• Believing puts cannot be used inside blocks

5. Given a hash scores = { alice: 10, bob: 15, carol: 12 }, how can you use each to print each name and score in the format Name: Score?

hard

A. scores.each { |name| puts "#{name.capitalize}: #{score}" }

B. scores.each { |score, name| puts "#{name}: #{score}" }

C. scores.each do |name| puts "#{name}: #{scores[name]}" end

D. scores.each do |name, score| puts "#{name.capitalize}: #{score}" end

Solution

1. Step 1: Understand hash iteration with each

   When iterating a hash with each, two block variables receive the key and value respectively.

2. Step 2: Use correct variable order and string formatting

   scores.each do |name, score| puts "#{name.capitalize}: #{score}" end correctly uses |name, score| and prints with #{name.capitalize}: #{score}.

3. Final Answer:

   scores.each do |name, score| puts "#{name.capitalize}: #{score}" end -> Option D

4. Quick Check:

   Hash each uses two vars: key, value [OK]

Hint: Hash each needs two vars: |key, value| [OK]

Common Mistakes:

• Swapping key and value variables
• Using only one block variable for hash
• Not capitalizing the name correctly