Hash creation with symbols and strings in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a hash with mixed keys

What is the output of this Ruby code?

h = { :name => "Alice", "age" => 30 }
puts h[:name]
puts h["age"]

Ruby

h = { :name => "Alice", "age" => 30 }
puts h[:name]
puts h["age"]

A nil\nnil

B Alice\n

C 30\nAlice

D Alice\n30

💡 Hint

Remember that symbol keys and string keys are different in Ruby hashes.

In Ruby, :name and "name" are different keys. The hash has :name and "age" keys. So h[:name] returns "Alice" and h["age"] returns 30.

❓ Predict Output

intermediate

Hash key lookup with symbol vs string

What will this Ruby code output?

h = { name: "Bob", "name" => "Carol" }
puts h[:name]
puts h["name"]

Ruby

h = { name: "Bob", "name" => "Carol" }
puts h[:name]
puts h["name"]

A Bob\nCarol

B Carol\nBob

C Bob\nBob

D Carol\nCarol

💡 Hint

Check how Ruby treats symbol keys and string keys separately.

The hash has two keys: :name and "name". They are different keys with different values. So h[:name] returns "Bob" and h["name"] returns "Carol".

🔧 Debug

advanced

Why does this hash key lookup fail?

This Ruby code returns nil for the second puts. Why?

h = { :city => "Paris" }
puts h["city"]

Ruby

h = { :city => "Paris" }
puts h["city"]

A Because "city" is not a valid key type

B Because the hash is empty

C Because :city and "city" are different keys in Ruby hashes

D Because the hash keys must be strings only

💡 Hint

Think about the difference between symbols and strings as keys.

In Ruby, symbol keys and string keys are distinct. The hash has :city key but no "city" key, so h["city"] returns nil.

📝 Syntax

advanced

Identify the syntax error in hash creation

Which option contains a syntax error when creating a Ruby hash with symbol and string keys?

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

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

C h = { :a => 1, "b" => 2 }

D h = { a: 1, b: 2 }

💡 Hint

Check the correct syntax for symbol keys in hashes.

Option B uses :a: which is invalid syntax. The correct symbol key syntax is either :a => 1 or a: 1.

🚀 Application

expert

Count keys by type in a mixed hash

Given this Ruby hash:

h = { name: "Eve", "age" => 28, city: "NY", "country" => "USA" }

How many keys are symbols and how many are strings?

Ruby

h = { name: "Eve", "age" => 28, city: "NY", "country" => "USA" }
symbol_count = h.keys.count { |k| k.is_a?(Symbol) }
string_count = h.keys.count { |k| k.is_a?(String) }
puts "Symbols: #{symbol_count}, Strings: #{string_count}"

A Symbols: 2, Strings: 2

B Symbols: 3, Strings: 1

C Symbols: 0, Strings: 4

D Symbols: 4, Strings: 0

💡 Hint

Look carefully at the keys and their types.

The hash has keys :name and :city as symbols, and "age" and "country" as strings, so 2 symbols and 2 strings.