Hash methods (keys, values, each) in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of keys and values methods

What is the output of this Ruby code?

Ruby

h = {a: 1, b: 2, c: 3}
puts h.keys.inspect
puts h.values.inspect

A

[:a, :b, :c]
["1", "2", "3"]

B

["a", "b", "c"]
[1, 2, 3]

C

["a", "b", "c"]
["1", "2", "3"]

D

[:a, :b, :c]
[1, 2, 3]

💡 Hint

Remember that Ruby symbols are shown with a colon and strings with quotes.

The keys method returns an array of the hash's keys as symbols, and values returns an array of the values as they are stored (integers here).

❓ Predict Output

intermediate

Using each to iterate over a hash

What does this Ruby code print?

Ruby

h = {x: 10, y: 20}
h.each do |key, value|
  puts "#{key}:#{value}" 
end

A

10:x
20:y

B

x:10
y:20

C

[:x, 10]
[:y, 20]

D

x => 10
y => 20

💡 Hint

Look at how the block variables are used inside the string.

The each method yields each key and value pair. The code prints key and value separated by a colon on separate lines.

🧠 Conceptual

advanced

Behavior of keys method on empty hash

What is the result of calling keys on an empty hash in Ruby?

A An empty array []

B nil

C Raises an error

D An array with one nil element [nil]

💡 Hint

Think about what keys exist in an empty hash.

Calling keys on an empty hash returns an empty array because there are no keys.

❓ Predict Output

advanced

Effect of modifying hash inside each

What is the output of this Ruby code?

Ruby

h = {a: 1, b: 2}
h.each do |k, v|
  h[k] = v * 2
end
puts h.inspect

A {:a=>1, :b=>4}

B {:a=>1, :b=>2}

C {:a=>2, :b=>4}

D RuntimeError: can't modify hash during iteration

💡 Hint

Think about whether modifying values during iteration is allowed.

Modifying the values of existing keys during each is allowed. The values get doubled.

❓ Predict Output

expert

Output of nested each with keys and values

What is printed by this Ruby code?

Ruby

h = {one: [1, 2], two: [3, 4]}
h.each do |key, values|
  values.each do |v|
    puts "#{key}-#{v}"
  end
end

A

one-1
one-2
two-3
two-4

B

one-1
two-2
one-3
two-4

C

one-1
one-2
one-3
one-4

D

1-one
2-one
3-two
4-two

💡 Hint

Look carefully at the nested iteration and string interpolation.

The outer each iterates keys and arrays. The inner each iterates values, printing key-value pairs separated by a dash.