Match method and MatchData in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of Match method with capture groups

What is the output of this Ruby code?

Ruby

result = /Hello (\w+)/.match("Hello World")
puts result[1]

A nil

B Hello

C World

D Error

💡 Hint

Remember that the first capture group is accessed with index 1.

The regex captures the word after 'Hello '. The match method returns a MatchData object. Accessing result[1] returns the first captured group, which is 'World'.

❓ Predict Output

intermediate

MatchData object methods

What does this Ruby code print?

Ruby

m = /(\d+)-(\d+)/.match("123-456")
puts m.begin(1)

A 0

B 4

C 3

D Error

💡 Hint

begin(n) returns the start index of the nth capture group.

The first capture group (\d+) matches '123' starting at index 0. The second capture group matches '456' starting at index 4. So m.begin(1) returns 0, m.begin(2) returns 4. The code prints 0.

❓ Predict Output

advanced

Using MatchData to extract named captures

What is the output of this Ruby code?

Ruby

pattern = /(?<area>\d{3})-(?<number>\d{4})/
match = pattern.match("555-1234")
puts match[:area]

A 1234

B 555

C area

D nil

💡 Hint

Named captures can be accessed with symbols.

The regex defines named groups 'area' and 'number'. Accessing match[:area] returns the string matched by the 'area' group, which is '555'.

❓ Predict Output

advanced

Match method returns nil when no match

What is the output of this Ruby code?

Ruby

result = /cat/.match("dog")
puts result.nil?

A true

B nil

C false

D Error

💡 Hint

If the pattern does not match, match returns nil.

The string 'dog' does not contain 'cat', so match returns nil. puts result.nil? prints true.

🧠 Conceptual

expert

Understanding MatchData captures and indexing

Given the Ruby code below, what is the value of match[0], match[1], and match[2] respectively?

Ruby

match = /(\w+)-(\d+)/.match("code-123")

A "code", "code-123", "123"

B "code", "-", "123"

C "code-123", "-", "123"

D "code-123", "code", "123"

💡 Hint

match[0] is the entire matched string; match[1] and match[2] are capture groups.

match[0] returns the full matched string 'code-123'. match[1] returns the first capture group '\w+' which is 'code'. match[2] returns the second capture group '\d+' which is '123'.