Default values for missing keys in Ruby - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a hash with a default value of 0.

Ruby

counts = Hash.new([1])

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

A''

Bfalse

Cnil

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using nil as default value returns nil for missing keys, not 0.

Using empty string '' sets default to a string, not a number.

Using Hash.new(0) sets the default value to 0 for any missing key.

2fill in blank

medium

Complete the code to create a hash with a default value of an empty array.

Ruby

groups = Hash.new([1])

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

A{}

B[]

Cnil

D0

Attempts:

3 left

💡 Hint

Common Mistakes

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

Using nil means missing keys return nil, not an array.

Using Hash.new([]) sets the default value to the same empty array for all missing keys.

3fill in blank

hard

Fix the error in the code to correctly set a default value that is a new empty array for each missing key.

Ruby

groups = Hash.new { |hash, key| hash[[1]] = [] }

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

Akey

Bhash

Cgroups

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'hash' instead of 'key' as the index causes an error.

Using 'value' is incorrect because the block only has hash and key parameters.

The block receives the hash and the missing key. Assigning hash[key] = [] creates a new empty array for each missing key.

4fill in blank

hard

Fill both blanks to create a hash that counts occurrences of words.

Ruby

counts = Hash.new([1])
words.each do |word|
  counts[word] = counts[word] [2] 1
end

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

A0

B+

C-

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-' subtracts instead of adding.

Using '*' multiplies, which is incorrect for counting.

Setting default to 0 allows counting. Using '+' adds 1 to the current count.

5fill in blank

hard

Fill all three blanks to create a hash with default value as a new array and add elements to it.

Ruby

groups = Hash.new { |hash, [1]| hash[[2]] = [3] }
groups[:fruits] << 'apple'

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

Akey

C[]

D{}

Attempts:

3 left

💡 Hint

Common Mistakes

Using '{}' assigns an empty hash instead of an array.

Using different names for the key parameter causes errors.

The block takes the missing key as 'key'. Assigning hash[key] = [] creates a new empty array for each missing key, allowing elements to be added.