Any?, all?, none? predicates in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of any? with a block

What is the output of this Ruby code?

Ruby

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

A RuntimeError

B false

C nil

D true

💡 Hint

Think about whether any number in the array is even.

The any? method returns true if at least one element satisfies the block condition. Here, none are even, so it returns false.

❓ Predict Output

intermediate

Result of all? without a block

What does this Ruby code print?

Ruby

values = [true, 1, 'hello']
puts values.all?

A nil

B false

C true

D ArgumentError

💡 Hint

Without a block, all? checks truthiness of each element.

The all? method without a block returns true if all elements are truthy. Here, all elements are truthy, so it prints true.

❓ Predict Output

advanced

none? with a block returning false

What is the output of this Ruby code?

Ruby

words = ['apple', 'banana', 'cherry']
result = words.none? { |w| w.length > 5 }
puts result

A true

B nil

C TypeError

D false

💡 Hint

Check if any word has length greater than 5.

The none? method returns true if no elements satisfy the block. Here, 'banana' and 'cherry' have length > 5, so none? returns false.

🧠 Conceptual

advanced

Understanding all? with mixed truthy and falsy values

Given the array [nil, true, false], what does all? return when called without a block?

A false

B true

C nil

D ArgumentError

💡 Hint

Remember that all? checks truthiness of each element.

Since nil and false are falsy in Ruby, all? returns false when called without a block.

❓ Predict Output

expert

Complex predicate with any?, all?, none?

What is the output of this Ruby code?

Ruby

data = [0, nil, false, '']
result = [
  data.any?,
  data.all?,
  data.none?
]
puts result.inspect

A [true, false, false]

B [false, false, true]

C [true, true, false]

D [false, true, false]

💡 Hint

Recall that only false and nil are falsy; zero and empty string are truthy.

any? returns true because 0 and '' are truthy.
all? returns false because nil and false are falsy.
none? returns false because there are truthy elements (0 and '').

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?