Select/filter for filtering in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Ruby code using select?

Consider the following Ruby code that filters numbers greater than 3 from an array. What will be printed?

Ruby

numbers = [1, 2, 3, 4, 5]
result = numbers.select { |n| n > 3 }
puts result.inspect

A [1, 2, 3]

B [4, 5]

C []

D [3, 4, 5]

💡 Hint

Remember, select keeps elements where the block returns true.

The select method returns a new array containing all elements for which the block returns true. Here, only 4 and 5 are greater than 3.

❓ Predict Output

intermediate

What does this filter code output?

Given this Ruby code using filter (alias for select), what is the output?

Ruby

words = ['apple', 'banana', 'cherry', 'date']
filtered = words.filter { |w| w.length == 5 }
puts filtered.inspect

A ["apple"]

B ["apple", "cherry"]

C ["banana", "date"]

D ["apple", "banana", "cherry", "date"]

💡 Hint

Check the length of each word carefully.

Only 'apple' has exactly 5 letters. 'cherry' has 6 letters, so it is not included.

❓ Predict Output

advanced

What is the output when filtering hashes with select?

What will this Ruby code print?

Ruby

people = [{name: 'Alice', age: 30}, {name: 'Bob', age: 20}, {name: 'Carol', age: 25}]
adults = people.select { |p| p[:age] >= 25 }
puts adults.map { |p| p[:name] }.inspect

A ["Alice", "Carol"]

B ["Bob", "Carol"]

C ["Alice", "Bob"]

D ["Carol"]

💡 Hint

Select people whose age is 25 or more.

Alice is 30 and Carol is 25, so both are included. Bob is 20, so excluded.

❓ Predict Output

advanced

What error does this code raise?

What error will this Ruby code raise when trying to filter with a wrong block?

Ruby

numbers = [1, 2, 3]
result = numbers.select { |n| n > '2' }
puts result.inspect

A ArgumentError

B No error, outputs [3]

C TypeError

D NoMethodError

💡 Hint

Compare integer with string causes a problem.

Comparing integer n with string '2' using > causes a TypeError in Ruby.

🧠 Conceptual

expert

How many elements are in the result of this chained filter?

Given this Ruby code, how many elements are in the final array?

Ruby

arr = [10, 15, 20, 25, 30]
result = arr.select { |x| x > 10 }.select { |x| x % 10 == 0 }

A 1

B 3

C 4

D 2

💡 Hint

First filter keeps numbers greater than 10, second keeps multiples of 10.

Numbers greater than 10 are [15, 20, 25, 30]. Among these, multiples of 10 are 20 and 30, so 2 elements.