Ruby for And each Loops

In programming, we often need to go through a list of values one at a time. For example, we may want to print each item in a collection (array, hash, etc.) or add numbers in a range.

Ruby provides two primary ways to do this:

• The for loop
• The each loop

Both loops are used to go through (iterate over) each item in a collection or a range.

Let's explore each of them and see how they're related, starting with the for loop.

Ruby for Loop

The for loop is used to iterate over a range or a collection (like arrays or hashes), one at a time. Its syntax is:

for variable in collection
  # Code to execute
end

Here,

• collection - A range of values, or a collection of values like arrays or hashes.
• variable - A placeholder that takes the value of each element in the collection during each iteration.

Here's how it works:

• The for loop iterates over the elements of the collection.
• In every iteration, the variable takes the value of the current collection element. It is then reassigned to the next element in the following iteration.
• The loop ends once all the elements have been iterated over.

Note: Many Ruby programmers prefer the each loop over the for loop when iterating over collections.

Example 1: Ruby for Loop with Range

for num in 4..6
  puts num
end

Output

4
5
6

Here, the for loop iterates over the range 4..6. As a result, the loop runs three times over the numbers 4, 5, and 6.

In each iteration of the loop, the variable num takes values from 4 to 6, which is then printed to the screen. Here's how it works:

Example 2: Ruby for Loop with Array

people = ["Bob", "Alex", "Sharon", "Cassie"]

for person in people
  puts person
end

Output

Bob
Alex
Sharon
Cassie

Here, the for loop iterates over the people array. In each iteration of the loop, the variable person takes the corresponding element of the array. Here's how this works:

Example 3: Ruby for Loop with Hash

# Create a hash named 'person'
# "name", "age", and "city" are keys
# "Alice", 30, and "Paris" are the corresponding values

person = { "name" => "Alice", "age" => 30, "city" => "Paris" }

for key, value in person
  puts "#{key}: #{value}"
end

Output

name: Alice
age: 30
city: Paris

In this example, we created a hash named person. Then, we used a for loop to iterate over the hash.

In each iteration of the loop, the key and value variables of the loop take a key-value pair from the hash. Here's how it works:

Ruby each Loop

The each loop is another way to iterate over collections. It is preferred by Ruby developers over the for loop due to its readability. Its syntax is:

collection.each do |item|
  # Code using item
end

Here,

• collection - A collection of values like arrays or hashes.
• item - A placeholder that takes the value of each element in the collection during each iteration.

Example 4: Ruby each Loop with Range

(4..6).each do |num|
  puts num
end

Output

4
5
6

Here, the each loop iterates over the range 4..6. As a result, the loop runs three times over the numbers 4, 5, and 6.

In each iteration of the loop, the variable num takes values from 4 to 6, which is then printed to the screen. Here's how it works:

Example 5: Ruby each Loop with Array

people = ["Bob", "Alex", "Sharon", "Cassie"]

people.each do |person|
  puts person
end

Output

Bob
Alex
Sharon
Cassie

Here, the each loop runs once for each item in the people array.

In each iteration, the person variable takes a single element from the people array, which is similar to how our for loop example works:

Example 6: Ruby each Loop with Hash

# Create a hash named 'person'
# "name", "age", and "city" are keys
# "Alice", 30, and "Paris" are the corresponding values

person = { "name" => "Alice", "age" => 30, "city" => "Paris" }

person.each do |key, value|
  puts "#{key}: #{value}"
end

Output

name: Alice
age: 30
city: Paris

Here, the each loop runs once for each item in the person hash.

In each iteration, the key and value variables of the loop take a key-value pair from the hash. Here's how it works:

collection.each { |item| # code using item }

# With range
(1..3).each { |i| puts i }

# With array
[4, 5, 6].each { |i| puts i }

my_hash = { "name" => "Revan", "age" => 40 }

# With hash
my_hash.each { |key, value| puts "#{key}: #{value}" }

1
2
3
4
5
6
name: Revan
age: 40

for i in 1..3
  puts "i = #{i}"
end

# Valid: Using i outside the for loop
puts "i = #{i}"

i = 1
i = 2
i = 3
i = 3

(1..3).each do |i|
  puts "i = #{i}"
end

# Invalid: Using i outside the each loop
puts "i = #{i}"

i = 1
i = 2
i = 3
main.rb:6:in '<main>': undefined local variable or method 'i' for main (NameError)