Array creation methods in Ruby - Cheat Sheet & Quick Revision

Recall & Review

beginner

How do you create an empty array in Ruby?

You create an empty array by using square brackets with nothing inside: [].

beginner

What does Array.new(3) do in Ruby?

It creates a new array with 3 elements, all set to nil by default: [nil, nil, nil].

beginner

How can you create an array with 5 zeros using Array.new?

Use Array.new(5, 0). This creates an array with 5 elements, each set to 0: [0, 0, 0, 0, 0].

intermediate

What is the difference between Array.new(3, []) and Array.new(3) { [] }?

The first creates an array with 3 references to the same empty array (shared object). The second creates 3 separate empty arrays (different objects).

beginner

How do you create an array from a range in Ruby?

Use the to_a method on a range. For example, (1..5).to_a creates [1, 2, 3, 4, 5].

What does Array.new(4) return?

A An error

B [0, 0, 0, 0]

C [nil, nil, nil, nil]

D [[], [], [], []]

Array.new(4) creates an array with 4 elements, all set to nil by default.

How do you create an array of 3 empty arrays, each a separate object?

A Array.new(3, [])

B Array.new(3) { [] }

C [[], [], []]

D Both B and C

Using a block with Array.new(3) { [] } or writing [[], [], []] creates separate empty arrays.

What does (5..8).to_a produce?

A [5, 6, 7, 8]

B [5, 6, 7]

C [6, 7, 8]

D An error

The range 5..8 includes 5, 6, 7, and 8. to_a converts it to an array with these elements.

What is the result of Array.new(3, 'a')?

A ['a', 'b', 'c']

B ['a', 'a', 'a']

C [nil, nil, nil]

D An error

It creates an array with 3 elements, each set to the string 'a'.

Which method creates an empty array?

A All of the above

B Array.new(0)

C Array.new

D []

All these create an empty array in Ruby.

Explain three different ways to create arrays in Ruby and when you might use each.

Think about empty arrays, arrays with repeated values, and arrays with unique objects.

Describe the difference between Array.new(3, []) and Array.new(3) { [] } in Ruby.

Consider what happens if you change one element inside the arrays.