sub and gsub in R Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of sub() with repeated pattern

What is the output of this R code snippet?

R Programming

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

A "orange apple apple"

B "orange orange orange"

C "apple apple orange"

D "apple orange apple"

💡 Hint

Remember that sub() replaces only the first match.

The sub() function replaces only the first occurrence of the pattern. So only the first "apple" becomes "orange".

❓ Predict Output

intermediate

Output of gsub() with multiple replacements

What will this R code print?

R Programming

text <- "cat bat rat"
result <- gsub("at", "og", text)
print(result)

A "cat bat rat"

B "cog bog rog"

C "cog bat rat"

D "cat bog rat"

💡 Hint

gsub() replaces all matches in the string.

The gsub() function replaces all occurrences of the pattern. Here, "at" in each word is replaced by "og".

🔧 Debug

advanced

Why does this sub() call not replace anything?

Consider this R code: text <- "Hello World" result <- sub("world", "Earth", text) print(result) Why does the output remain "Hello World"?

R Programming

text <- "Hello World"
result <- sub("world", "Earth", text)
print(result)

A Because sub() requires the pattern to be a regular expression object

B Because sub() only replaces the first word in the string

C Because sub() is case-sensitive and "world" does not match "World"

D Because the replacement string "Earth" is invalid

💡 Hint

Check the capitalization of the pattern and the text.

The sub() function is case-sensitive by default. The pattern "world" does not match "World" because of the capital W.

📝 Syntax

advanced

Identify the syntax error in this gsub() usage

Which option contains a syntax error when trying to replace "dog" with "cat" in the string "dog dog dog"?

R Programming

text <- "dog dog dog"
result <- gsub(pattern, replacement, text)

A gsub("dog", "cat", text)

B sub("dog", "cat", text)

C )txet ,"tac" ,"god"(busg

D gsub("dog", cat, text)

💡 Hint

Check if the replacement argument is a string or a variable.

Option D uses cat without quotes, which is treated as a variable or function, causing an error if undefined.

🧠 Conceptual

expert

Difference in output length between sub() and gsub()

Given the string "a1b2c3d4", what is the length of the string after applying sub("[0-9]", "X", text) and gsub("[0-9]", "X", text) respectively?

A sub() result length: 8, gsub() result length: 8

B sub() result length: 7, gsub() result length: 7

C sub() result length: 8, gsub() result length: 4

D sub() result length: 7, gsub() result length: 8

💡 Hint

Replacing characters with another single character keeps string length the same.

Both sub() and gsub() replace digits with "X" without changing string length. So both results have length 8.