Why hashes are used everywhere in Ruby - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a hash with a key 'name' and value 'Ruby'.

Ruby

person = { :name => [1] }

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

A"Ruby"

BRuby

C:Ruby

Dname

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to put quotes around string values.

Using a symbol instead of a string for the value.

In Ruby, hash values can be strings. Here, the value for the key :name is the string "Ruby".

2fill in blank

medium

Complete the code to access the value of the key :age from the hash.

Ruby

person = { age: 25 }
age = person[[1]]

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

Aage

B"age"

C:age

D25

Attempts:

3 left

💡 Hint

Common Mistakes

Using a string "age" instead of symbol :age.

Using the value 25 instead of the key.

To access a value in a Ruby hash using a symbol key, use the symbol :age inside the brackets.

3fill in blank

hard

Fix the error in the code to add a new key-value pair :city => 'Tokyo' to the hash.

Ruby

person = { name: "Ruby" }
person[1] = "Tokyo"

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

A.city

B[:city]

Ccity

Attempts:

3 left

💡 Hint

Common Mistakes

Using dot notation which is invalid for hashes.

Using the key without brackets.

To add or update a key-value pair in a Ruby hash, use the syntax hash[:key] = value.

4fill in blank

hard

Fill both blanks to create a hash with keys :a and :b and values 1 and 2.

Ruby

numbers = { [1]: 1, [2]: 2 }

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

Aa

B1

Cb

D2

Attempts:

3 left

💡 Hint

Common Mistakes

Using numbers as keys instead of symbols.

Putting quotes around keys.

Keys in Ruby hashes can be symbols written as :a and :b. Here, we use the shorthand syntax with keys a and b.

5fill in blank

hard

Fill all three blanks to create a hash with keys :x, :y and values 10, 20, and access the value of :y.

Ruby

coords = { [1]: [2], [3]: 20 }
y_value = coords[:y]

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

Ax

B10

Cy

D20

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up keys and values.

Using strings instead of symbols for keys.

The hash has keys :x and :y with values 10 and 20. We access the value of :y using coords[:y].

Practice

1. Why are hashes used everywhere in Ruby?

easy

A. Because they only store numbers efficiently

B. Because they store data as key-value pairs for easy access

C. Because they are the only data structure in Ruby

D. Because they automatically sort data alphabetically

Solution

1. Step 1: Understand what hashes store

   Hashes store data as pairs where each key points to a value, making it easy to find information.

2. Step 2: Recognize why this is useful in Ruby

   This key-value structure helps organize data clearly and access it quickly, which is why hashes are popular.

3. Final Answer:

   Because they store data as key-value pairs for easy access -> Option B

4. Quick Check:

   Hashes = key-value pairs [OK]

Hint: Hashes connect keys to values for easy data lookup [OK]

Common Mistakes:

• Thinking hashes only store numbers
• Believing hashes are the only Ruby data structure
• Assuming hashes sort data automatically

2. Which of the following is the correct syntax to create a hash in Ruby?

easy

A. my_hash = { name: 'Alice', age: 30 }

B. my_hash = [ 'name' => 'Alice', 'age' => 30 ]

C. my_hash = ( name: 'Alice', age: 30 )

D. my_hash = < name: 'Alice', age: 30 >

Solution

1. Step 1: Identify Ruby hash syntax

   Ruby hashes use curly braces {} with key-value pairs separated by commas. Keys can be symbols like :name.

2. Step 2: Check each option

   my_hash = { name: 'Alice', age: 30 } uses correct curly braces and symbol keys. Others use wrong brackets or invalid syntax.

3. Final Answer:

   my_hash = { name: 'Alice', age: 30 } -> Option A

4. Quick Check:

   Curly braces and symbol keys = correct hash syntax [OK]

Hint: Use curly braces and colons for keys in Ruby hashes [OK]

Common Mistakes:

• Using square brackets instead of curly braces
• Using parentheses instead of braces
• Using angle brackets which are invalid

3. What will be the output of this Ruby code?

person = { name: 'Bob', age: 25 }
puts person[:name]

medium

A. 25

B. name

C. nil

D. Bob

Solution

1. Step 1: Understand the hash and key access

   The hash stores :name with value 'Bob' and :age with 25. Accessing person[:name] retrieves 'Bob'.

2. Step 2: Check the puts output

   puts prints the value of person[:name], which is 'Bob'.

3. Final Answer:

   Bob -> Option D

4. Quick Check:

   person[:name] = 'Bob' [OK]

Hint: Access hash values by keys with square brackets [OK]

Common Mistakes:

• Confusing key with value
• Using string keys instead of symbol keys
• Expecting the key name to print

4. Find the error in this Ruby code using a hash:

settings = { theme: 'dark', font_size: 12 }
puts settings['theme']

medium

A. Missing comma between key-value pairs

B. Hash keys must be strings, not symbols

C. Using string key instead of symbol key causes nil output

D. Syntax error due to missing curly braces

Solution

1. Step 1: Check hash keys and access method

   The hash uses symbol keys (:theme), but the code tries to access with a string key ('theme').

2. Step 2: Understand the result of wrong key type

   Accessing with a string key returns nil because the keys don't match.

3. Final Answer:

   Using string key instead of symbol key causes nil output -> Option C

4. Quick Check:

   Symbol keys need symbol access [OK]

Hint: Match key types exactly when accessing hashes [OK]

Common Mistakes:

• Mixing string and symbol keys
• Assuming keys auto-convert types
• Ignoring nil return on missing keys

5. You want to store user info with keys :name, :age, and :email. Which hash usage best supports easy updates and clear code?

hard

A. user = { name: 'Eve', age: 28, email: '[e-mail]' }

B. user = [ 'name' => 'Eve', 'age' => 28, 'email' => '[e-mail]' ]

C. user = { 'name', 'Eve', 'age', 28, 'email', '[e-mail]' }

D. user = ( name: 'Eve', age: 28, email: '[e-mail]' )

Solution

1. Step 1: Identify correct hash syntax for storing key-value pairs

   user = { name: 'Eve', age: 28, email: '[e-mail]' } uses a hash with symbol keys and values inside curly braces, which is clear and easy to update.

2. Step 2: Evaluate other options for correctness and clarity

   user = [ 'name' => 'Eve', 'age' => 28, 'email' => '[e-mail]' ] uses array syntax incorrectly, C is invalid syntax, and D uses parentheses which is not valid for hashes.

3. Final Answer:

   user = { name: 'Eve', age: 28, email: '[e-mail]' } -> Option A

4. Quick Check:

   Curly braces with symbol keys = best practice [OK]

Hint: Use curly braces and symbol keys for clear, update-friendly hashes [OK]

Common Mistakes:

• Using arrays instead of hashes
• Incorrect syntax with parentheses
• Mixing key-value pairs without proper separators