Method chaining patterns in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of chained string methods

What is the output of this Ruby code using method chaining?

Ruby

result = "  hello world  ".strip.upcase.reverse
puts result

A "DLROW OLLEH"

B "dlrow olleh"

C "HELLO WORLD"

D " HELLO WORLD "

💡 Hint

Think about what each method does in order: strip, upcase, then reverse.

The strip method removes spaces at the start and end, upcase converts all letters to uppercase, and reverse reverses the string. So the final output is the reversed uppercase string without spaces.

❓ Predict Output

intermediate

Chained array transformations output

What does this Ruby code print?

Ruby

numbers = [1, 2, 3, 4, 5]
result = numbers.select(&:odd?).map { |n| n * 10 }.join(",")
puts result

A "2,4"

B "1,3,5"

C "10,30,50"

D "20,40"

💡 Hint

First select odd numbers, then multiply each by 10, then join with commas.

select(&:odd?) picks odd numbers [1,3,5]. map { |n| n * 10 } multiplies each by 10 giving [10,30,50]. join(",") makes a string "10,30,50".

🔧 Debug

advanced

Identify the error in method chaining

What error does this Ruby code raise?

Ruby

result = "123abc".to_i.to_s.reverse
puts result

A NoMethodError: undefined method `reverse' for Integer

B No error, outputs "321"

C TypeError: can't convert String into Integer

D ArgumentError: invalid value for Integer()

💡 Hint

Check the return types of each method in the chain.

to_i converts string to integer 123, to_s converts back to string "123", then reverse reverses it to "321". No error occurs.

🔧 Debug

advanced

Which option raises a NoMethodError in method chaining?

Which of these Ruby code snippets will raise a NoMethodError?

A "HELLO".upcase!.reverse

B "hello".upcase.reverse

C "test".split.map(&:upcase)

D "example".reverse.upcase

💡 Hint

Bang methods like upcase! return nil if the string is not modified.

Option A: "HELLO".upcase! returns nil because the string is already uppercase (no mutation). Then nil.reverse raises NoMethodError. Options B, C, and D execute without error.

🚀 Application

expert

Count words with method chaining

Using method chaining, which code correctly counts how many words in the string have length greater than 3?

Ruby

text = "Ruby is fun and powerful"

A

count = text.split.filter { |w| w.length > 3 }.size
puts count

B

count = text.split.map { |w| w.length > 3 }.count
puts count

C

count = text.split.reduce(0) { |acc, w| acc + (w.length > 3 ? 1 : 0) }
puts count

D

count = text.split.select { |w| w.length > 3 }.count
puts count

💡 Hint

Select words longer than 3 characters, then count them.

Option D uses select to filter words with length > 3 ("Ruby", "powerful"), then count returns 2. Option D raises NoMethodError (filter undefined in standard Ruby). Option D maps to booleans and count (no arg) returns array size 5. Option D works (2) but is less idiomatic than enumerator methods.