Match method and MatchData in Ruby - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to find the first match of the pattern in the string.

Ruby

result = 'hello123'.match([1])

Drag options to blanks, or click blank then click option'

A'\d+'

B/\d+/

C/hello/

D'hello'

Attempts:

3 left

💡 Hint

Common Mistakes

Using a string instead of a regular expression.

Forgetting to use slashes around the pattern.

The match method expects a regular expression, so /\d+/ correctly matches digits.

2fill in blank

medium

Complete the code to get the matched substring from the MatchData object.

Ruby

match = 'abc123'.match(/\d+/)
matched_text = match[1]

Drag options to blanks, or click blank then click option'

A.string

B.to_s

C[1]

D[0]

Attempts:

3 left

💡 Hint

Common Mistakes

Using index 1 which returns the first capture group, not the full match.

Using .string which returns the original string, not the match.

Accessing index 0 of MatchData returns the entire matched substring.

3fill in blank

hard

Fix the error in the code to safely check if a pattern matches the string.

Ruby

if 'test123'.match(/\d+/)[1]
  puts 'Match found'
else
  puts 'No match'
end

Drag options to blanks, or click blank then click option'

A!= false

B== nil

C!= nil

D== true

Attempts:

3 left

💡 Hint

Common Mistakes

Checking '== true' which is incorrect because match returns MatchData or nil.

Checking '!= false' which is not reliable for nil checks.

match returns nil if no match, so checking '!= nil' confirms a match.

4fill in blank

hard

Complete the code to create a hash of words and their lengths for words longer than 3 characters.

Ruby

words = ['cat', 'house', 'dog', 'elephant']
lengths = {word=> len(word) for word in words if word[1] 3}

Drag options to blanks, or click blank then click option'

A.to_sym =>

B.length >

C.length <

D=>

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' in the condition.

Using '.to_sym =>' which is not needed here.

The hash uses 'word => len(word)' and the condition checks if word.length > 3.

5fill in blank

hard

Fill all three blanks to extract named captures from a string using MatchData.

Ruby

text = 'Name: John, Age: 30'
pattern = /Name: (?<name>\w+), Age: (?<age>\d+)/
match = text.match([1])
name = match[2][:name]
age = match[3][:age]

Drag options to blanks, or click blank then click option'

Apattern

B.named_captures

C.captures

D.[]

Attempts:

3 left

💡 Hint

Common Mistakes

Using .named_captures which returns a hash, not accessed with [:name].

Using .captures which returns an array, not a hash.

Use the pattern variable in match, then access named captures with match[:name] and match[:age].

Practice

1. What does the Ruby match method return when it finds a pattern in a string?

easy

A. A MatchData object containing details of the match

B. The matched substring as a string

C. An array of all matched substrings

D. A boolean value true

Solution

1. Step 1: Understand the purpose of match

   The match method searches a string for a pattern and returns information about the match.

2. Step 2: Identify the return type when a match is found

   It returns a MatchData object, which holds details like matched text and position.

3. Final Answer:

   A MatchData object containing details of the match -> Option A

4. Quick Check:

   match returns MatchData [OK]

Hint: Remember: match returns MatchData, not just string [OK]

Common Mistakes:

• Thinking it returns just the matched string
• Assuming it returns an array of matches
• Believing it returns true/false

2. Which of the following is the correct syntax to use the match method on a string str to find the pattern /abc/?

easy

A. /abc/.match(str)

B. match(str, /abc/)

C. str.match(/abc/)

D. str.match = /abc/

Solution

1. Step 1: Recall the method call format

   The match method is called on a string object with a regex pattern as argument.

2. Step 2: Check each option's syntax

   str.match(/abc/) correctly calls str.match(/abc/). match(str, /abc/) is invalid syntax. /abc/.match(str) reverses receiver and argument. str.match = /abc/ tries assignment, which is wrong.

3. Final Answer:

   str.match(/abc/) -> Option C

4. Quick Check:

   Correct method call = str.match(/abc/) [OK]

Hint: Call match on string with regex inside parentheses [OK]

Common Mistakes:

• Using match as a standalone function
• Swapping receiver and argument
• Trying to assign with =

3. What will be the output of the following Ruby code?

result = "hello123".match(/\d+/)
puts result[0]

medium

A. 123

B. hello

C. nil

D. An error is raised

Solution

1. Step 1: Understand the regex pattern

   The pattern /\d+/ matches one or more digits in the string.

2. Step 2: Analyze the match and output

   In "hello123", digits "123" match. result[0] accesses the matched substring "123".

3. Final Answer:

   123 -> Option A

4. Quick Check:

   Digits matched = "123" [OK]

Hint: Access matched text with result[0] after match [OK]

Common Mistakes:

• Expecting the whole string as output
• Confusing nil with empty string
• Not using index 0 to get matched text

4. Consider this Ruby code snippet:

text = "abc"
match = text.match(/d/)
puts match[0]

What is the problem here?

medium

A. The regex pattern is invalid

B. Trying to access match[0] when match is nil

C. The string text is empty

D. The match method does not exist for strings

Solution

1. Step 1: Check the regex pattern and string

   The pattern /d/ looks for 'd' in "abc", which is not present, so match returns nil.

2. Step 2: Identify the error cause

   Trying to do match[0] when match is nil causes a NoMethodError.

3. Final Answer:

   Trying to access match[0] when match is nil -> Option B

4. Quick Check:

   Accessing [0] on nil causes error [OK]

Hint: Check if match is nil before accessing [OK]

Common Mistakes:

• Assuming pattern is invalid
• Ignoring that match can be nil
• Thinking match method is missing

5. You want to extract the first word starting with a capital letter from the string "today is a Sunny day" using match. Which code correctly does this and prints the matched word?

hard

A. puts "today is a Sunny day".match(/[A-Z]+/)[0]

B. puts "today is a Sunny day".match(/[a-z]\w*/)[0]

C. puts "today is a Sunny day".match(/\b\w+/)[0]

D. puts "today is a Sunny day".match(/[A-Z]\w*/)[0]

Solution

1. Step 1: Understand the regex requirements

   We want the first word starting with a capital letter. Pattern /[A-Z]\w*/ matches a capital letter followed by zero or more word characters.

2. Step 2: Analyze each option

   puts "today is a Sunny day".match(/[A-Z]\w*/)[0] matches correctly and returns the first capitalized word "Sunny". puts "today is a Sunny day".match(/[a-z]\w*/)[0] matches lowercase start, first is "today", wrong. puts "today is a Sunny day".match(/\b\w+/)[0] matches any word, first is "today", not capitalized. puts "today is a Sunny day".match(/[A-Z]+/)[0] matches only consecutive capital letters, first is "S", not full word.

3. Final Answer:

   puts "today is a Sunny day".match(/[A-Z]\w*/)[0] -> Option D

4. Quick Check:

   Capitalized word match = puts "today is a Sunny day".match(/[A-Z]\w*/)[0] [OK]

Hint: Use regex starting with [A-Z] and access [0] from match [OK]

Common Mistakes:

• Using lowercase letter class instead of uppercase
• Matching only letters without full word
• Not accessing matched text with [0]