Each for iteration in Ruby - Step-by-Step Execution

Concept Flow - Each for iteration

Start with collection

↓

Pick next element

↓

Run block with element

↓

More elements?

No→End iteration

↩Back to Pick next element

The 'each' method takes each element from a collection one by one and runs the given block of code with it until all elements are processed.

Execution Sample

Ruby

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

This code goes through each number in the list and prints double its value.

Execution Table

Iteration	num value	Action	Output
1	1	Run block with num=1	2
2	2	Run block with num=2	4
3	3	Run block with num=3	6
-	-	No more elements, iteration ends	-

💡 All elements processed, 'each' loop ends

Variable Tracker

Variable	Start	After 1	After 2	After 3	Final
num	nil	1	2	3	nil

Key Moments - 2 Insights

Why does 'num' change each iteration?

'num' takes the value of the current element from the collection each time the block runs, as shown in execution_table rows 1 to 3.

What happens after the last element is processed?

The loop stops because there are no more elements, as shown in the last row of execution_table where iteration ends.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of 'num' during iteration 2?

A 1

B 2

C 3

D nil

💡 Hint

Check the 'num value' column in the second row of execution_table.

At which iteration does the loop stop running the block?

A After iteration 1

B After iteration 2

C After iteration 3

D It never stops

💡 Hint

Look at the exit note and the last row in execution_table.

If the array was empty, what would happen to the 'num' variable?

A It would never be set and block never runs

B It would be set to nil and block runs once

C It would be set to 0

D It would cause an error

💡 Hint

Refer to variable_tracker and understand that 'num' changes only when block runs.

Concept Snapshot

Ruby 'each' method:
- Goes through each element in a collection
- Runs the block with current element as variable
- Stops after last element
- Variable inside block changes each iteration
- No output unless block prints or returns

Full Transcript

The Ruby 'each' method takes a collection like an array and runs a block of code for each element. In the example, numbers 1, 2, and 3 are processed one by one. The variable 'num' holds the current element's value during each iteration. The block prints double the number. After all elements are done, the loop ends. If the array is empty, the block never runs and 'num' stays nil.

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