sub and gsub in R Programming - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to replace the first occurrence of 'cat' with 'dog' in the string.

R Programming

result <- sub([1], "dog", "cat and cat")

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

A"cat"

B"dog"

C"and"

D"cat and cat"

Attempts:

3 left

💡 Hint

Common Mistakes

Using the replacement string as the pattern.

Using the whole string as the pattern.

The sub function replaces the first match of the pattern, so we use "cat" as the pattern to replace.

2fill in blank

medium

Complete the code to replace all occurrences of 'cat' with 'dog' in the string.

R Programming

result <- gsub([1], "dog", "cat and cat")

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

A"cat"

B"dog"

C"and"

D"cat and cat"

Attempts:

3 left

💡 Hint

Common Mistakes

Using sub instead of gsub for all replacements.

Using the replacement string as the pattern.

The gsub function replaces all matches of the pattern, so the pattern should be "cat" to replace all occurrences.

3fill in blank

hard

Fix the error in the code to replace the first 'a' with 'o' in the string.

R Programming

result <- sub([1], "o", "banana")

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

Aa

B"a"

C'a'

Dbanana

Attempts:

3 left

💡 Hint

Common Mistakes

Using unquoted letters as patterns.

Using the whole string as the pattern.

The pattern must be a string, so it needs to be in quotes like "a".

4fill in blank

hard

Fill both blanks to replace all digits with '#' in the string.

R Programming

result <- gsub([1], [2], "Phone: [phone]")

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

A"[0-9]"

B"#"

C"-"

D"Phone"

Attempts:

3 left

💡 Hint

Common Mistakes

Using sub instead of gsub to replace all digits.

Using wrong pattern that doesn't match digits.

The pattern "[0-9]" matches any digit, and "#" is the replacement character.

5fill in blank

hard

Fill all three blanks to replace all vowels with '*' in the string.

R Programming

result <- gsub([1], [2], [3])

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

A"[aeiouAEIOU]"

B"*"

C"Hello World"

D"[0-9]"

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong pattern that doesn't match vowels.

Using sub instead of gsub to replace all vowels.

The pattern "[aeiouAEIOU]" matches all vowels, "*" is the replacement, and "Hello World" is the input string.

Practice

1. What is the main difference between sub and gsub in R?

easy

A. sub works only with numbers, gsub works only with text.

B. sub replaces all matches, gsub replaces only the first match.

C. sub replaces only the first match, gsub replaces all matches.

D. sub modifies the original string, gsub returns a new string.

Solution

1. Step 1: Understand sub behavior

   sub replaces only the first occurrence of the pattern in the string.

2. Step 2: Understand gsub behavior

   gsub replaces all occurrences of the pattern in the string.

3. Final Answer:

   sub replaces only the first match, gsub replaces all matches. -> Option C

4. Quick Check:

   sub = first match, gsub = all matches [OK]

Hint: Remember: sub = first, gsub = global (all) [OK]

Common Mistakes:

• Confusing which function replaces all matches
• Thinking sub modifies original string in place
• Assuming gsub only replaces first match

2. Which of the following is the correct syntax to replace the first occurrence of "cat" with "dog" in the string "cat and cat" using sub?

easy

A. sub("cat", "dog", "cat and cat")

B. sub("dog", "cat", "cat and cat")

C. gsub("cat", "dog", "cat and cat")

D. replace("cat", "dog", "cat and cat")

Solution

1. Step 1: Identify correct function and parameters

   sub takes pattern, replacement, and the string in that order.

2. Step 2: Check the parameters match the question

   We want to replace "cat" with "dog" in "cat and cat" using sub.

3. Final Answer:

   sub("cat", "dog", "cat and cat") -> Option A

4. Quick Check:

   Correct syntax with sub and parameters [OK]

Hint: sub(pattern, replacement, string) is the order [OK]

Common Mistakes:

• Swapping pattern and replacement arguments
• Using gsub instead of sub for first occurrence
• Using a non-existent function like replace

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

text <- "apple apple apple"
result <- sub("apple", "orange", text)
print(result)

medium

A. "orange orange orange"

B. "orange apple apple"

C. "apple orange apple"

D. "apple apple orange"

Solution

1. Step 1: Understand sub replaces first match only

   The first "apple" in the string is replaced by "orange".

2. Step 2: Apply replacement to the string

   Result becomes "orange apple apple" because only the first "apple" changes.

3. Final Answer:

   "orange apple apple" -> Option B

4. Quick Check:

   sub replaces first match only [OK]

Hint: sub changes only first match, not all [OK]

Common Mistakes:

• Thinking sub replaces all matches
• Confusing sub with gsub
• Expecting all words to change

4. The following code is intended to replace all spaces with underscores in the string "hello world example" but does not work as expected. What is the error?

text <- "hello world example"
new_text <- sub(" ", "_", text)
print(new_text)

medium

A. The print statement is incorrect syntax.

B. The pattern " " is invalid, use "\\s" instead.

C. The replacement string should be "-" not "_".

D. sub replaces only the first space, use gsub to replace all spaces.

Solution

1. Step 1: Identify function behavior

   sub replaces only the first match, so only the first space is replaced.

2. Step 2: Suggest correct function for all replacements

   To replace all spaces, gsub should be used instead of sub.

3. Final Answer:

   sub replaces only the first space, use gsub to replace all spaces. -> Option D

4. Quick Check:

   Use gsub for all matches, sub for first only [OK]

Hint: Use gsub to replace all matches, not sub [OK]

Common Mistakes:

• Using sub when gsub is needed
• Thinking space pattern is invalid
• Changing replacement character unnecessarily

5. You have a vector of strings: c("cat123", "dog456", "bird789"). You want to remove all digits from each string. Which R code correctly does this using gsub?

hard

A. gsub("[0-9]", "", c("cat123", "dog456", "bird789"))

B. sub("[0-9]", "", c("cat123", "dog456", "bird789"))

C. gsub("[^0-9]+", "", c("cat123", "dog456", "bird789"))

D. sub("\\d", "", c("cat123", "dog456", "bird789"))

Solution

1. Step 1: Identify pattern to remove digits

   The pattern "[0-9]" matches any single digit; "\\d+" matches one or more digits.

2. Step 2: Choose function to replace all digits

   Use gsub to replace all digit occurrences, not just the first.

3. Step 3: Check options

   gsub("[0-9]", "", c("cat123", "dog456", "bird789")) uses gsub with "[0-9]" which removes all digits correctly.

4. Final Answer:

   gsub("[0-9]", "", c("cat123", "dog456", "bird789")) -> Option A

5. Quick Check:

   gsub + digit pattern removes all digits [OK]

Hint: Use gsub with digit pattern to remove all digits [OK]

Common Mistakes:

• Using sub instead of gsub, removing only first digit
• Incorrect regex pattern for digits
• Confusing escape sequences in regex