Array methods (length, include?, flatten) in Ruby - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to get the number of elements in the array.

Ruby

numbers = [1, 2, 3, 4, 5]
count = numbers.[1]
puts count

Drag options to blanks, or click blank then click option'

Atotal

Bsize

Ccount

Dlength

Attempts:

3 left

💡 Hint

Common Mistakes

Using a method that does not exist like 'total'.

Confusing 'length' with 'include?'.

The length method returns the number of elements in an array.

2fill in blank

medium

Complete the code to check if the array contains the number 3.

Ruby

numbers = [1, 2, 3, 4, 5]
has_three = numbers.[1](3)
puts has_three

Drag options to blanks, or click blank then click option'

Ahas?

Binclude?

Ccontains?

Dexists?

Attempts:

3 left

💡 Hint

Common Mistakes

Using methods that do not exist like 'contains?'.

Forgetting the question mark at the end of 'include?'.

The include? method checks if an array has a specific element and returns true or false.

3fill in blank

hard

Fix the error in the code to flatten the nested array into a single array.

Ruby

nested = [[1, 2], [3, 4], [5]]
flat = nested.[1]
puts flat.inspect

Drag options to blanks, or click blank then click option'

Aflatten

Bflatten!

Cflat!

Dflat

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'flatten!' which modifies the original array instead of returning a new one.

Using non-existent methods like 'flat' or 'flat!'.

The flatten method returns a new array that is a one-dimensional flattening of the original nested array.

4fill in blank

hard

Fill both blanks to create a hash with words as keys and their lengths as values, only for words longer than 3 letters.

Ruby

words = ["apple", "cat", "banana", "dog"]
lengths = words.each_with_object({}) do |word, h|
  if word.[1] [2] 3
    h[word] = word.[1]
  end
end
puts lengths

Drag options to blanks, or click blank then click option'

A.length

B>

Clength

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '.length' which causes a syntax error (double dot).

Using '<' instead of '>' for the condition.

Use length to get the word length and > to check if it is greater than 3.

5fill in blank

hard

Fill all three blanks to create a hash with uppercase words as keys and their lengths as values, only for words longer than 3 letters.

Ruby

words = ["apple", "cat", "banana", "dog"]
lengths = words.each_with_object({}) do |word, h|
  if word.[2] [3] 3
    h[word[1]] = word.[2]
  end
end
puts lengths

Drag options to blanks, or click blank then click option'

A.upcase

Blength

C>

Dcapitalize

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'capitalize' instead of 'upcase' for uppercase keys.

Using '<' instead of '>' in the condition.

Use .upcase to make keys uppercase, length to get word length, and > to filter words longer than 3 letters.

Practice

1. What does the length method do when called on an array in Ruby?

easy

A. Returns the number of elements in the array

B. Checks if an element exists in the array

C. Flattens nested arrays into a single array

D. Removes duplicate elements from the array

Solution

1. Step 1: Understand the purpose of length

   The length method counts how many items are inside an array.

2. Step 2: Compare with other methods

   include? checks for presence, flatten merges nested arrays, so they do different things.

3. Final Answer:

   Returns the number of elements in the array -> Option A

4. Quick Check:

   length = count items [OK]

Hint: Remember length counts items, not checks or changes arrays [OK]

Common Mistakes:

• Confusing length with include? method
• Thinking length flattens nested arrays
• Assuming length removes duplicates

2. Which of the following is the correct syntax to check if the array arr includes the number 5?

easy

A. arr.include(5)

B. arr.includes?(5)

C. arr.has?(5)

D. arr.include?(5)

Solution

1. Step 1: Recall the correct method name and syntax

   The method to check presence is include? with a question mark at the end.

2. Step 2: Verify method call on array

   It should be called as arr.include?(5), not include or includes?.

3. Final Answer:

   arr.include?(5) -> Option D

4. Quick Check:

   Correct method is include? with question mark [OK]

Hint: Remember Ruby methods with ? end with a question mark [OK]

Common Mistakes:

• Omitting the question mark in include?
• Using incorrect method names like includes? or has?
• Using parentheses incorrectly

3. What is the output of the following Ruby code?

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

medium

A. 5

B. 3

C. 6

D. 7

Solution

1. Step 1: Apply flatten to the array

   The nested array [1, [2, 3], [4, [5]]] becomes [1, 2, 3, 4, 5] after flattening.

2. Step 2: Calculate the length of the flattened array

   The flattened array has 5 elements, so length returns 5.

3. Final Answer:

   5 -> Option A

4. Quick Check:

   Flattened array length = 5 [OK]

Hint: Flatten first, then count elements with length [OK]

Common Mistakes:

• Counting nested arrays as single elements
• Forgetting flatten changes nested arrays
• Miscounting elements after flatten

4. The following code is intended to check if the array nums contains the number 10, but it raises an error. What is the problem?

nums = [5, 10, 15]
if nums.include(10)
  puts "Found 10"
end

medium

A. The array should be flattened before checking

B. The method should be include? with a question mark

C. The number 10 should be a string "10"

D. The if statement syntax is incorrect

Solution

1. Step 1: Identify the method name error

   The method to check presence is include? with a question mark, not include.

2. Step 2: Understand why error occurs

   Calling include without question mark is undefined, causing an error.

3. Final Answer:

   The method should be include? with a question mark -> Option B

4. Quick Check:

   Use include? to check presence [OK]

Hint: Check method names carefully; include? needs question mark [OK]

Common Mistakes:

• Using include without question mark
• Thinking flatten is needed to check presence
• Confusing number and string types
• Miswriting if statement syntax

5. Given the nested array data = [[1, 2], [3, [4, 5]], 6], which Ruby code correctly flattens it and checks if the number 4 is included?

hard

A. data.include?(4.flatten)

B. data.include?(4).flatten

C. data.flatten.include?(4)

D. data.flatten.include(4)

Solution

1. Step 1: Flatten the nested array first

   Use data.flatten to convert nested arrays into a single-level array.

2. Step 2: Check if 4 is included in the flattened array

   Call include?(4) on the flattened array to get true or false.

3. Final Answer:

   data.flatten.include?(4) -> Option C

4. Quick Check:

   Flatten then include? is correct order [OK]

Hint: Flatten first, then check inclusion with include? [OK]

Common Mistakes:

• Calling include? before flatten
• Using include without question mark
• Trying to flatten the number 4
• Incorrect method chaining order