Array methods (length, include?, flatten) in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Ruby code using length?

Look at the array and the method used. What will be printed?

Ruby

arr = [1, 2, 3, 4, 5]
puts arr.length

A 5

B 4

C 6

D Error

💡 Hint

The length method tells how many items are in the array.

The array has 5 numbers, so length returns 5.

❓ Predict Output

intermediate

What does include? return here?

Check if the array contains the number 3.

Ruby

arr = [1, 2, 3, 4, 5]
puts arr.include?(3)

A false

B Error

C nil

D true

💡 Hint

The method include? returns true if the item is found.

Since 3 is in the array, include?(3) returns true.

❓ Predict Output

advanced

What is the output of flatten on a nested array?

This array has arrays inside. What will flatten do?

Ruby

arr = [1, [2, 3], [4, [5, 6]]]
puts arr.flatten.inspect

A [1, [2, 3], [4, [5, 6]]]

B [1, 2, 3, 4, 5, 6]

C [1, 2, 3, 4, [5, 6]]

D Error

💡 Hint

The flatten method removes all nested arrays and makes one flat array.

All nested arrays are merged into one single array with all elements.

❓ Predict Output

advanced

What is the length of the array after flattening?

Check the length of the array after using flatten.

Ruby

arr = [[1, 2], [3, 4], 5]
flat_arr = arr.flatten
puts flat_arr.length

A 5

B 3

C 4

D Error

💡 Hint

Flattening removes nested arrays, so count all individual elements.

The flattened array is [1, 2, 3, 4, 5], which has length 5.

🧠 Conceptual

expert

Which option causes an error when calling include??

One of these arrays will cause an error when calling include? with argument 3. Which one?

A arr = [1, 2, 3]; arr.include?(3)

B arr = [nil, false]; arr.include?(3)

C arr = nil; arr.include?(3)

D arr = []; arr.include?(3)

💡 Hint

Think about what happens if the variable is not an array.

Calling include? on nil causes a NoMethodError because nil has no such method.