Hash creation with symbols and strings in Ruby - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a hash with a symbol key :name and value "Alice".

Ruby

person = { [1] => "Alice" }

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

Aname:

B"name"

Cname

D:name

Attempts:

3 left

💡 Hint

Common Mistakes

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

Using a bare word name without quotes or colon.

The symbol :name is used as a key in the hash.

2fill in blank

medium

Complete the code to create a hash with a string key "age" and value 30.

Ruby

person = { [1] => 30 }

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

A:age

Bage

C"age"

Dage:

Attempts:

3 left

💡 Hint

Common Mistakes

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

Using a bare word age without quotes or colon.

The string "age" is used as a key in the hash.

3fill in blank

hard

Fix the error in the hash creation by completing the code with the correct symbol key.

Ruby

person = { [1]: "Bob" }

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

Aname

B"name"

C:name

Dname:

Attempts:

3 left

💡 Hint

Common Mistakes

Using :name: which is invalid syntax.

Using "name": which is a string key, not symbol shorthand.

When using the symbol key shorthand, the key is written without the colon prefix, just the name.

4fill in blank

hard

Fill both blanks to create a hash with symbol key :city and string key "country".

Ruby

location = { [1] => "Paris", [2] => "France" }

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

A:city

B"city"

C"country"

D:country

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up symbol and string keys.

Using bare words without colon or quotes.

The first key is a symbol :city, the second key is a string "country".

5fill in blank

hard

Fill all three blanks to create a hash with symbol keys :name and :age, and string key "city".

Ruby

person = { [1] => "Eve", [2] => 28, [3] => "Berlin" }

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

A:name

B:age

C"city"

D"age"

Attempts:

3 left

💡 Hint

Common Mistakes

Using string "age" instead of symbol :age.

Mixing up quotes and colons for keys.

The keys are symbol :name, symbol :age, and string "city".

Practice

1. Which of the following is a valid way to create a Ruby hash with symbol keys?

easy

A. { name => "Alice", age => 30 }

B. { "name": "Alice", "age": 30 }

C. { :name => "Alice", "age": 30 }

D. { name: "Alice", age: 30 }

Solution

1. Step 1: Understand symbol key syntax

   In Ruby, symbol keys can be written as name: value without the rocket (=>) syntax.

2. Step 2: Check each option's syntax

   { name: "Alice", age: 30 } uses symbol keys with colon syntax correctly. { "name": "Alice", "age": 30 } uses string keys with colon, which is invalid. { :name => "Alice", "age": 30 } uses rocket syntax for the symbol key correctly but attempts colon syntax after a string key, which is invalid. { name => "Alice", age => 30 } uses bare words without colon or rocket, which is invalid.

3. Final Answer:

   { name: "Alice", age: 30 } -> Option D

4. Quick Check:

   Symbol keys use colon syntax = { name: "Alice", age: 30 } [OK]

Hint: Symbol keys use colon after name, not quotes or bare words [OK]

Common Mistakes:

• Using quotes around symbol keys with colon syntax
• Omitting colon or rocket for keys
• Mixing string and symbol keys without proper syntax

2. Which of the following hash definitions will cause a syntax error in Ruby?

easy

A. { name => "Bob", age => 25 }

B. { :name => "Bob", :age => 25 }

C. { "name" => "Bob", "age" => 25 }

D. { name: "Bob", age: 25 }

Solution

1. Step 1: Review valid key syntax

   Symbol keys can be written as :name => or name:. String keys must be quoted and use rocket syntax.

2. Step 2: Identify invalid syntax

   { name => "Bob", age => 25 } uses bare words as keys without colon or rocket, which is invalid and causes syntax error.

3. Final Answer:

   SyntaxError -> Option A

4. Quick Check:

   Bare words as keys need colon or rocket [OK]

Hint: Keys must be symbols with colon or strings with quotes and rocket [OK]

Common Mistakes:

• Using bare words as keys without colon or rocket
• Mixing string keys without quotes
• Confusing colon placement for symbols

3. What is the output of the following Ruby code?

person = { name: "Carol", "age" => 28 }
puts person[:name]
puts person["age"]

medium

A. Carol
28

B. Carol

C.
28

D. nil
nil

Solution

1. Step 1: Understand hash keys and access

   The hash has a symbol key :name and a string key "age". Accessing with matching key types returns values.

2. Step 2: Evaluate each puts statement

   person[:name] returns "Carol". person["age"] returns 28. Both print on separate lines.

3. Final Answer:

   Carol 28 -> Option A

4. Quick Check:

   Match key types to get values = Carol 28 [OK]

Hint: Use matching symbol or string keys to access hash values [OK]

Common Mistakes:

• Accessing string key with symbol or vice versa
• Expecting mixed keys to be interchangeable
• Forgetting keys are type-sensitive

4. Identify the error in this Ruby hash creation:

data = { :city => "Paris", country: "France", "population" => 2148327, state } 

medium

A. Hash keys cannot mix symbols and strings

B. Incorrect symbol syntax for :city

C. Missing value for key 'state'

D. String keys must use colon syntax

Solution

1. Step 1: Check each key-value pair

   Keys :city, country, and "population" have values. The key 'state' is written without a value, which is invalid.

2. Step 2: Identify syntax error

   Every key in a hash must have a corresponding value. Missing value for 'state' causes syntax error.

3. Final Answer:

   Missing value for key 'state' -> Option C

4. Quick Check:

   All keys need values in hash = Missing value for key 'state' [OK]

Hint: Every key must have a value; check for missing pairs [OK]

Common Mistakes:

• Leaving keys without values
• Confusing symbol and string key syntax
• Assuming mixed keys cause errors

5. Given the array arr = [["name", "Dave"], [:age, 40], ["city", "NY"]], which code correctly converts it into a hash with symbol keys where possible?

hard

A. hash = arr.to_h

B. hash = arr.map { |k, v| [k.to_sym, v] }.to_h

C. hash = arr.map { |k, v| [k, v] }.to_h

D. hash = arr.map { |k, v| [k.to_s, v] }.to_h

Solution

1. Step 1: Understand the array structure

   The array has pairs with keys as strings or symbols. We want all keys as symbols where possible.

2. Step 2: Convert keys to symbols

   hash = arr.map { |k, v| [k.to_sym, v] }.to_h converts each key to symbol using k.to_sym before creating the hash, ensuring keys are symbols.

3. Step 3: Check other options

   hash = arr.to_h keeps keys as is (mixed). hash = arr.map { |k, v| [k, v] }.to_h keeps keys as is without conversion. hash = arr.map { |k, v| [k.to_s, v] }.to_h converts all keys to strings, not symbols.

4. Final Answer:

   hash = arr.map { |k, v| [k.to_sym, v] }.to_h -> Option B

5. Quick Check:

   Use to_sym on keys to get symbol keys [OK]

Hint: Use map with to_sym on keys to get symbol keys [OK]

Common Mistakes:

• Not converting string keys to symbols
• Using to_s instead of to_sym
• Assuming to_h converts keys automatically