Each as the primary iterator in Ruby - Step-by-Step Execution

Concept Flow - Each as the primary iterator

Start with collection

↓

Call each method

↓

Take first element

↓

Execute block with element

↓

Move to next element

↓

More elements?

No→End iteration

↩Back to Execute block

The each method takes one element at a time from a collection and runs the given block on 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

Step	Current Element (num)	Block Execution	Output	Next Action
1	1	puts 1 * 2	2	Move to next element
2	2	puts 2 * 2	4	Move to next element
3	3	puts 3 * 2	6	No more elements, end iteration

💡 All elements processed, each iteration ends

Variable Tracker

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

Key Moments - 3 Insights

Why does the variable 'num' change each time in the block?

Because 'each' takes one element at a time from the collection and assigns it to 'num' before running the block, as shown in steps 1 to 3 in the execution_table.

What happens after the last element is processed?

The iteration stops because there are no more elements to assign to 'num', as explained in the exit_note and step 3 of the execution_table.

Does 'each' change the original collection?

No, 'each' only reads elements one by one and runs the block; it does not modify the original collection.

Visual Quiz - 3 Questions

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

A 1

B 3

C 2

D nil

💡 Hint

Check the 'Current Element (num)' column at step 2 in the execution_table.

At which step does the iteration end according to the execution_table?

A Step 1

B After Step 3

C Step 3

D Step 2

💡 Hint

Look at the 'Next Action' column and the exit_note for when iteration stops.

If the array had one more element, how would the execution_table change?

A There would be an extra step with that element as 'num'.

B The iteration would stop earlier.

C The output would be empty.

D The variable 'num' would not change.

💡 Hint

Refer to how each element is processed step-by-step in the execution_table.

Concept Snapshot

each method syntax:
collection.each do |element|
  # code using element
end

Behavior:
- Takes one element at a time
- Runs block with that element
- Continues until all elements done
- Does not modify original collection

Full Transcript

The 'each' method in Ruby goes through every item in a collection one by one. For each item, it assigns it to a variable (like 'num') and runs the code inside the block. This continues until all items are processed. The original collection stays the same. In the example, numbers 1, 2, and 3 are doubled and printed. The variable 'num' changes each step to the current element. When no elements remain, the iteration ends.

Practice

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

easy

A. It returns a new array with modified items.

B. It runs a block of code once for every item in the array.

C. It changes the array by removing items.

D. It sorts the array in ascending order.

Solution

1. Step 1: Understand the purpose of each

   The each method is used to run a block of code for every item in a collection like an array.

2. Step 2: Check what each does to the array

   It does not change or sort the array; it simply processes each item one by one.

3. Final Answer:

   It runs a block of code once for every item in the array. -> Option B

4. Quick Check:

   each runs code on each item [OK]

Hint: Remember: each processes items, does not change array [OK]

Common Mistakes:

• Thinking each modifies the array
• Confusing each with methods like map
• Assuming each returns a new array

2. Which of the following is the correct syntax to use each on an array numbers to print each number?

easy

A. each numbers { |num| puts num }

B. numbers.each do num puts num end

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

D. numbers.each |num| puts num

Solution

1. Step 1: Identify correct block syntax with each

   The correct syntax uses each followed by a block with { |variable| ... } or do |variable| ... end.

2. Step 2: Check each option

   numbers.each { |num| puts num } uses numbers.each { |num| puts num } which is correct. Others have syntax errors or wrong order.

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 { |item| ... } or each do |item| ... end [OK]

Common Mistakes:

• Writing each numbers instead of numbers.each
• Missing block delimiters like braces or do-end
• Not using pipes | | around block variable

3. What is the output of this Ruby code?

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

medium

A. APPLE
BANANA
CHERRY

B. apple
banana
cherry

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

D. Error: undefined method upcase for fruit

Solution

1. Step 1: Understand what each does with puts fruit.upcase

   The each method runs the block for each fruit, printing the uppercase version.

2. Step 2: Check output line by line

   It prints 'APPLE', then 'BANANA', then 'CHERRY' each on a new line.

3. Final Answer:

   APPLE BANANA CHERRY -> Option A

4. Quick Check:

   each prints uppercase fruits [OK]

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

Common Mistakes:

• Thinking each returns a new array
• Expecting lowercase output
• Confusing puts with returning a list

4. What is wrong with this Ruby code snippet?

items = [1, 2, 3]
items.each do item
  puts item * 2
end

medium

A. Array items is empty

B. Using do instead of braces is invalid

C. Cannot multiply numbers inside each

D. Missing pipes around block variable: should be |item|

Solution

1. Step 1: Check block variable syntax in each do block

   When using do with each, the block variable must be inside pipes: do |item|.

2. Step 2: Identify the error

   The code misses pipes around item, causing a syntax error.

3. Final Answer:

   Missing pipes around block variable: should be |item| -> Option D

4. Quick Check:

   Block variables need pipes | | [OK]

Hint: Always put block variables inside | | with each do [OK]

Common Mistakes:

• Omitting pipes around block variables
• Thinking do is invalid with each
• Assuming multiplication inside each is wrong

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, score| puts "#{name.capitalize}: #{score}" }

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

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

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

Solution

1. Step 1: Understand each on a hash

   When using each on a hash, the block receives two variables: key and value.

2. Step 2: Match variables and format output

   The key is the name (symbol), value is the score. Use name.capitalize to print the name nicely.

3. Final Answer:

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

4. Quick Check:

   Hash each uses key, value pairs [OK]

Hint: Hash each block gets two vars: key and value [OK]

Common Mistakes:

• Swapping key and value variables
• Using only one block variable for hash
• Trying to capitalize a number