Any?, all?, none? predicates in Ruby - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if any number in the array is even.

Ruby

numbers = [1, 3, 5, 6, 7]
result = numbers.[1]? { |n| n.even? }
puts result

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

Aselect

Ball

Cnone

Dany

Attempts:

3 left

💡 Hint

Common Mistakes

Using all? instead of any? which checks all elements.

Using none? which checks if no elements match.

The any? method returns true if at least one element meets the condition.

2fill in blank

medium

Complete the code to check if all words in the array start with a capital letter.

Ruby

words = ["Apple", "Banana", "Cherry"]
result = words.[1]? { |word| word[0] == word[0].upcase }
puts result

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

Anone

Ball

Cany

Dfind

Attempts:

3 left

💡 Hint

Common Mistakes

Using any? which returns true if just one element matches.

Using none? which returns true if no elements match.

The all? method returns true only if every element meets the condition.

3fill in blank

hard

Fix the error in the code to check if no numbers in the array are negative.

Ruby

numbers = [0, 1, 2, 3]
result = numbers.[1]? { |n| n < 0 }
puts result

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

Aany

Ball

Cnone

Dfind

Attempts:

3 left

💡 Hint

Common Mistakes

Using any? which returns true if any element matches.

Using all? which requires all elements to match.

The none? method returns true if no elements satisfy the condition.

4fill in blank

hard

Fill both blanks to create a hash of words and their lengths, including only words longer than 3 letters.

Ruby

words = ["cat", "elephant", "dog", "lion"]
lengths = { [1] => [2] for word in words if word.length > 3 }
puts lengths

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

Aword

Bword.length

Cword.size

Dword.upcase

Attempts:

3 left

💡 Hint

Common Mistakes

Using word.upcase as a key or value incorrectly.

Using word.size instead of word.length (both work but only one is correct here).

The hash keys are the words, and the values are their lengths using word.length.

5fill in blank

hard

Fill all three blanks to create a hash of uppercase words and their lengths, including only words longer than 3 letters.

Ruby

words = ["cat", "elephant", "dog", "lion"]
lengths = { [1] => [2] for word in words if [2] [3] 3 }
puts lengths

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

Aword.upcase

Bword.length

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using < instead of > in the condition.

Using word instead of word.upcase as keys.

The keys are uppercase words, values are their lengths, and the condition filters words longer than 3 letters.

Practice

1.

Which Ruby method returns true if at least one element in a collection meets a condition?

easy

A. all?

B. any?

C. none?

D. each?

Solution

1. Step 1: Understand the meaning of any?

   any? returns true if at least one element satisfies the condition.

2. Step 2: Compare with other methods

   all? requires all elements to satisfy, none? requires none to satisfy, and each? is not a Ruby predicate method.

3. Final Answer:

   any? -> Option B

4. Quick Check:

   any? = at least one true [OK]

Hint: any? means at least one true element [OK]

Common Mistakes:

• Confusing any? with all?
• Thinking none? means at least one
• Using each? which is not a predicate

2.

Which of the following is the correct syntax to check if all elements in an array are even numbers?

numbers = [2, 4, 6, 8]
# Choose the correct line below

easy

A. numbers.all? { |n| n.even? }

B. numbers.none? { |n| n.even? }

C. numbers.any? { |n| n.even? }

D. numbers.each? { |n| n.even? }

Solution

1. Step 1: Identify the method to check all elements

   To verify every element meets a condition, use all?.

2. Step 2: Confirm the block checks evenness

   The block { |n| n.even? } correctly tests if each number is even.

3. Final Answer:

   numbers.all? { |n| n.even? } -> Option A

4. Quick Check:

   all? checks every element [OK]

Hint: Use all? with a block to check every item [OK]

Common Mistakes:

• Using any? instead of all?
• Using none? which checks for no matches
• Using each? which is not a predicate

3.

What is the output of the following Ruby code?

words = ["apple", "banana", "cherry"]
result = words.none? { |w| w.length > 6 }
puts result

medium

A. true

B. false

C. nil

D. SyntaxError

Solution

1. Step 1: Evaluate the block condition for each word

   Check if any word has length greater than 6: "banana" (6 letters) is not >6, "cherry" (6 letters) is not >6, "apple" (5 letters) is not >6.

2. Step 2: Determine if none? returns true or false

   Since no word has length > 6, none? returns true. But "banana" and "cherry" have length exactly 6, not greater than 6.

3. Step 3: Re-examine condition carefully

   None have length > 6, so none? returns true.

4. Final Answer:

   true -> Option A

5. Quick Check:

   none? means no elements match condition [OK]

Hint: none? returns true if no elements match condition [OK]

Common Mistakes:

• Confusing none? with any?
• Miscounting string lengths
• Assuming none? returns false if some equal condition

4.

Identify the error in this Ruby code snippet:

numbers = [1, 3, 5, 7]
puts numbers.all? { |n| n % 2 == 0 }

What is the output and why?

medium

A. true because all numbers are even

B. nil because no return value

C. SyntaxError due to block misuse

D. false because none of the numbers are even

Solution

1. Step 1: Analyze the array and condition

   The array contains odd numbers: 1, 3, 5, 7. The condition checks if each number is even (n % 2 == 0).

2. Step 2: Evaluate all? with the condition

   Since none of the numbers are even, all? returns false.

3. Final Answer:

   false -> Option D

4. Quick Check:

   all? returns false if any element fails condition [OK]

Hint: all? needs every element true to return true [OK]

Common Mistakes:

• Thinking all? returns true if some elements match
• Expecting SyntaxError for correct block usage
• Confusing output with nil

5.

You have a list of user ages: ages = [12, 17, 20, 25, 30]. You want to check if none of the users are under 18 years old. Which Ruby code correctly performs this check?

hard

A. ages.any? { |age| age < 18 }

B. ages.all? { |age| age < 18 }

C. ages.none? { |age| age < 18 }

D. ages.none? { |age| age >= 18 }

Solution

1. Step 1: Understand the condition to check

   We want to confirm no user is under 18, meaning no age < 18.

2. Step 2: Choose the method that returns true if no elements match condition

   none? returns true if no elements satisfy the block condition.

3. Step 3: Verify the block condition

   The block { |age| age < 18 } checks if age is under 18.

4. Final Answer:

   ages.none? { |age| age < 18 } -> Option C

5. Quick Check:

   none? means no elements match condition [OK]

Hint: Use none? to confirm no elements meet condition [OK]

Common Mistakes:

• Using any? which checks if some match
• Using all? which requires all to match
• Reversing the condition inside none?