Array creation methods in Ruby - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create an empty array.

Ruby

arr = [1]

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

A[]

B{}

C()

Dnil

Attempts:

3 left

💡 Hint

Common Mistakes

Using curly braces {} creates a hash, not an array.

In Ruby, square brackets [] create an empty array.

2fill in blank

medium

Complete the code to create an array with numbers 1 to 5 using a range.

Ruby

arr = (1..[1]).to_a

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

A4

B6

C5

D10

Attempts:

3 left

💡 Hint

Common Mistakes

Using 4 excludes the number 5 from the array.

The range 1..5 includes numbers from 1 to 5. Calling to_a converts it to an array.

3fill in blank

hard

Fix the error in the code to create an array with 3 elements, all set to 0.

Ruby

arr = Array.new([1], 0)

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

A-1

B0

C5

D3

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 creates an empty array, not an array with elements.

Array.new(3, 0) creates an array with 3 elements, each set to 0.

4fill in blank

hard

Fill both blanks to create an array of 4 elements, each initialized to its index multiplied by 2.

Ruby

arr = Array.new([1]) { |[2]| [2] * 2 }

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

A4

Bi

Cindex

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Using 5 for size creates 5 elements, not 4.

Array.new(4) { |i| i * 2 } creates an array [0, 2, 4, 6].

5fill in blank

hard

Fill all three blanks to create an array of 3 elements, each a string 'item' followed by its index.

Ruby

arr = Array.new([1]) { |[2]| "[3]#{ [2] }" }

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

A3

Bi

Citem

Dindex

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'index' as string instead of variable name causes errors.

This code creates ["item0", "item1", "item2"] by combining the string 'item' with the index.

Practice

1. Which of the following is a correct way to create an empty array in Ruby?

easy

A. array()

B. []

C. {}

D. new Array()

Solution

1. Step 1: Understand Ruby array syntax

   In Ruby, arrays are created using square brackets [] for literals.

2. Step 2: Identify correct empty array syntax

   [] creates an empty array, while {} creates an empty hash, and the other options are not Ruby syntax.

3. Final Answer:

   [] -> Option B

4. Quick Check:

   Empty array = [] [OK]

Hint: Empty arrays use square brackets [] in Ruby [OK]

Common Mistakes:

• Using curly braces {} which creates a hash
• Using parentheses like array() which is invalid
• Using JavaScript-like syntax new Array()

2. Which of the following is the correct syntax to create an array with 3 elements, all initialized to zero?

easy

A. Array.new(3, 0)

B. Array.new(0, 3)

C. Array(0, 3)

D. new Array(3, 0)

Solution

1. Step 1: Recall Array.new syntax

   In Ruby, Array.new(size, default_value) creates an array with given size and fills it with the default value.

2. Step 2: Check each option

   Array.new(3, 0) correctly creates [0, 0, 0]. Array.new(0, 3) creates an empty array since size is first argument. Options C and D are invalid syntax.

3. Final Answer:

   Array.new(3, 0) -> Option A

4. Quick Check:

   Array.new(3, 0) = [0, 0, 0] [OK]

Hint: Use Array.new(size, value) to create arrays with default values [OK]

Common Mistakes:

• Confusing Array.new arguments order
• Using invalid syntax like Array(0, 3)
• Trying JavaScript style new Array()

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

arr = Array.new(4) { |i| i * 2 }
puts arr.inspect

medium

A. [nil, nil, nil, nil]

B. [2, 4, 6, 8]

C. [0, 2, 4, 6]

D. [0, 0, 0, 0]

Solution

1. Step 1: Understand Array.new with block

   When Array.new is called with a block, it runs the block for each index, passing the index as i.

2. Step 2: Calculate each element

   For indices 0 to 3, the block returns i * 2: 0*2=0, 1*2=2, 2*2=4, 3*2=6.

3. Final Answer:

   [0, 2, 4, 6] -> Option C

4. Quick Check:

   Array with block fills elements by index * 2 [OK]

Hint: Array.new with block uses index to set each element [OK]

Common Mistakes:

• Assuming default value 0 for all elements
• Confusing block argument meaning
• Expecting nil values without block

4. The following code is intended to create an array of 3 separate empty arrays. What is the problem?

arr = Array.new(3, [])
arr[0] << 1
puts arr.inspect

medium

A. [[1], [1], [1]]

B. [[1], [], []]

C. [[], [], []]

D. SyntaxError

Solution

1. Step 1: Understand Array.new with default object

   Using Array.new(3, []) creates 3 references to the same empty array, not 3 separate arrays.

2. Step 2: Analyze mutation effect

   When arr[0] << 1 runs, it adds 1 to the shared array, so all elements show the change.

3. Final Answer:

   [[1], [1], [1]] -> Option A

4. Quick Check:

   Same object repeated causes all elements to change [OK]

Hint: Use block with Array.new for separate objects [OK]

Common Mistakes:

• Expecting separate arrays but all share one object
• Not using block form for unique elements
• Assuming << affects only one element

5. How can you create an array of 5 hashes, each with keys :a and :b initialized to 0, ensuring each hash is a separate object?

hard

A. Array(5) { {a: 0, b: 0} }

B. Array.new(5, {a: 0, b: 0})

C. [{a: 0, b: 0}] * 5

D. Array.new(5) { {a: 0, b: 0} }

Solution

1. Step 1: Understand object references in Array.new

   Using Array.new(5, {a: 0, b: 0}) or [{a: 0, b: 0}] * 5 repeats the same hash object 5 times.

2. Step 2: Use block form for unique hashes

   Using Array.new(5) { {a: 0, b: 0} } runs the block 5 times, creating 5 separate hashes.

3. Final Answer:

   Array.new(5) { {a: 0, b: 0} } -> Option D

4. Quick Check:

   Block form creates unique objects [OK]

Hint: Use block with Array.new for unique hashes [OK]

Common Mistakes:

• Using Array.new with default hash causes shared references
• Using multiplication operator with arrays of hashes
• Trying invalid Array() constructor syntax