Any?, all?, none? predicates in Ruby - Mini Project: Build & Apply

Using Any?, All?, and None? Predicates in Ruby

📖 Scenario: You are working on a simple system that checks a list of tasks to see if they meet certain conditions. This helps you decide if all tasks are done, if any task is urgent, or if none are overdue.

🎯 Goal: Build a Ruby program that uses any?, all?, and none? methods to check conditions on a list of tasks.

📋 What You'll Learn

Create an array of hashes called tasks with specific task details

Create a variable urgent_threshold to define urgency

Use any? to check if any task is urgent

Use all? to check if all tasks are completed

Use none? to check if no tasks are overdue

Print the results exactly as specified

💡 Why This Matters

🌍 Real World

Checking lists of tasks or items to quickly find if any, all, or none meet certain conditions is common in apps like to-do lists, inventory checks, or quality control.

💼 Career

Understanding these predicates helps in writing clean, readable code for filtering and decision-making in software development.

1

Create the tasks array

Create an array called tasks with these exact hashes: {name: 'Laundry', completed: false, days_overdue: 0}, {name: 'Homework', completed: true, days_overdue: 2}, {name: 'Grocery Shopping', completed: false, days_overdue: 5}

Ruby

# Create the tasks array with the given hashes
# Your code here

Hint

Use square brackets [] to create an array and curly braces {} for each task hash.

2

Set the urgency threshold

Create a variable called urgent_threshold and set it to 3 to define how many days overdue makes a task urgent

Ruby

tasks = [
  {name: 'Laundry', completed: false, days_overdue: 0},
  {name: 'Homework', completed: true, days_overdue: 2},
  {name: 'Grocery Shopping', completed: false, days_overdue: 5}
]
# Create urgent_threshold variable and set it to 3
# Your code here

Hint

Just assign the number 3 to the variable urgent_threshold.

3

Check tasks with any?, all?, and none?

Use any? on tasks to check if any task's days_overdue is greater than urgent_threshold and save it in any_urgent. Use all? to check if all tasks are completed and save it in all_completed. Use none? to check if no tasks have days_overdue greater than 0 and save it in none_overdue.

Ruby

tasks = [
  {name: 'Laundry', completed: false, days_overdue: 0},
  {name: 'Homework', completed: true, days_overdue: 2},
  {name: 'Grocery Shopping', completed: false, days_overdue: 5}
]
urgent_threshold = 3
# Use any?, all?, and none? to check tasks and save results
# Your code here

Hint

Use blocks with any?, all?, and none? to check the conditions on each task.

4

Print the results

Print the values of any_urgent, all_completed, and none_overdue each on its own line using puts.

Ruby

tasks = [
  {name: 'Laundry', completed: false, days_overdue: 0},
  {name: 'Homework', completed: true, days_overdue: 2},
  {name: 'Grocery Shopping', completed: false, days_overdue: 5}
]
urgent_threshold = 3

any_urgent = tasks.any? { |task| task[:days_overdue] > urgent_threshold }
all_completed = tasks.all? { |task| task[:completed] }
none_overdue = tasks.none? { |task| task[:days_overdue] > 0 }
# Print the results below
# Your code here

Hint

Use puts to print each variable on its own line.

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?