Merge and update methods in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Ruby code using merge?

Consider the following Ruby code snippet. What will be printed?

Ruby

h1 = {a: 1, b: 2}
h2 = {b: 3, c: 4}
result = h1.merge(h2)
puts result

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

B {:a=>1, :b=>3, :c=>4}

C {:a=>1, :b=>3}

D {:a=>1, :b=>2, :c=>4}

💡 Hint

Remember that merge returns a new hash with keys from both hashes, and values from the second hash overwrite the first.

The merge method combines two hashes. When keys overlap, the value from the second hash replaces the first. Here, :b is overwritten from 2 to 3.

❓ Predict Output

intermediate

What does update do to the original hash?

Given this Ruby code, what will be the value of h1 after update?

Ruby

h1 = {x: 10, y: 20}
h2 = {y: 30, z: 40}
h1.update(h2)
puts h1

A {:x=>10, :y=>30}

B {:x=>10, :y=>20, :z=>40}

C {:x=>10, :y=>20}

D {:x=>10, :y=>30, :z=>40}

💡 Hint

Update modifies the original hash by adding or replacing keys from the argument hash.

The update method changes h1 in place, adding :z and replacing :y with 30.

🔧 Debug

advanced

Why does this merge code raise an error?

This Ruby code raises an error. What is the cause?

Ruby

h1 = {a: 1, b: 2}
h2 = nil
h1.merge(h2)

A NoMethodError because nil does not have to_hash method

B ArgumentError because merge expects a hash argument

C TypeError because nil cannot be merged

D SyntaxError due to invalid syntax

💡 Hint

Check what merge expects as an argument and what nil is.

merge expects a hash or something convertible to a hash. nil does not respond to to_hash, causing NoMethodError.

❓ Predict Output

advanced

What is the output when using merge with a block?

What will this Ruby code print?

Ruby

h1 = {a: 100, b: 200}
h2 = {b: 300, c: 400}
result = h1.merge(h2) { |key, old_val, new_val| old_val + new_val }
puts result

A {:a=>100, :b=>500, :c=>400}

B {:a=>100, :b=>300, :c=>400}

C {:a=>100, :b=>200, :c=>400}

D {:a=>100, :b=>200, :c=>300}

💡 Hint

The block tells merge how to combine values for duplicate keys.

For key :b, the block adds old and new values: 200 + 300 = 500. Other keys are merged normally.

🧠 Conceptual

expert

How many keys are in the hash after this update?

Given this Ruby code, how many keys does h1 have after update?

Ruby

h1 = {a: 1, b: 2, c: 3}
h2 = {b: 4, d: 5, e: 6}
h1.update(h2)
h1.delete(:c)
h1[:f] = 7
puts h1.keys.size

A 6

B 4

C 5

D 3

💡 Hint

Count keys after update, delete, and adding a new key.

After update, h1 has keys :a, :b, :c, :d, :e. Then :c is deleted, leaving 4 keys. Adding :f makes 5 keys total.