strsplit in R Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of strsplit with multiple delimiters

What is the output of the following R code?

R Programming

text <- "apple,banana;cherry orange"
result <- strsplit(text, split = ",|;| ")
print(result)

A

[[1]]
[1] "apple" "banana" "cherry orange"

B

[[1]]
[1] "apple,banana;cherry orange"

C

[[1]]
[1] "apple" "banana;cherry" "orange"

D

[[1]]
[1] "apple" "banana" "cherry" "orange"

💡 Hint

The split argument can use regular expressions to split by multiple characters.

The split pattern ",|;| " means split at commas, semicolons, or spaces. So the string is split into four parts: apple, banana, cherry, and orange.

❓ Predict Output

intermediate

Result of strsplit with fixed = TRUE

What is the output of this R code?

R Programming

text <- "one.two.three"
result <- strsplit(text, split = ".", fixed = TRUE)
print(result)

A

[[1]]
[1] "one" "two" "three"

B

[[1]]
[1] "one.two.three"

C

[[1]]
[1] "one" "two.three"

D

[[1]]
[1] "one.two" "three"

💡 Hint

fixed = TRUE treats the split string literally, not as a regular expression.

With fixed = TRUE, the dot is treated as a normal character, so the string splits at each dot into three parts.

🔧 Debug

advanced

Identify the error in strsplit usage

What error does this R code produce?

R Programming

text <- "a,b,c"
result <- strsplit(text, split = c(",", ";"))
print(result)

A Error in strsplit: unused argument (split = c(",", ";"))

B Error in strsplit: 'split' must be a single string

C

[[1]]
[1] "a" "b" "c"

D NULL

💡 Hint

The split argument must be a single string, not a vector.

strsplit expects a single string pattern for splitting. Passing a vector causes an error about 'split' needing to be a single string.

🧠 Conceptual

advanced

Understanding strsplit output structure

What is the type and structure of the value returned by strsplit in R?

A A list where each element is a character vector of split parts

B A character vector of split parts

C A data frame with columns for each split part

D A matrix of characters with rows as split parts

💡 Hint

strsplit always returns a list, even if input is a single string.

strsplit returns a list. Each element corresponds to an input string and contains a character vector of the split parts.

❓ Predict Output

expert

Count of elements after splitting multiple strings

What is the length of the vector inside the first element of the list returned by this code?

R Programming

texts <- c("red,green,blue", "circle,square")
result <- strsplit(texts, split = ",")
length(result[[1]])

A 1

B 2

C 3

D Error: subscript out of bounds

💡 Hint

The first element corresponds to splitting the first string.

The first string "red,green,blue" splits into three parts, so length(result[[1]]) is 3.

Practice

1. What does the strsplit function in R do?

easy

A. It joins multiple strings into one string.

B. It counts the number of characters in a string.

C. It converts a string to uppercase letters.

D. It breaks a string into parts based on a separator.

Solution

1. Step 1: Understand the purpose of strsplit

   The strsplit function is designed to split a string into smaller parts using a specified separator.

2. Step 2: Compare options with function behavior

   Only It breaks a string into parts based on a separator. correctly describes this behavior. Options A, C, and D describe different string functions.

3. Final Answer:

   It breaks a string into parts based on a separator. -> Option D

4. Quick Check:

   strsplit splits strings = B [OK]

Hint: Remember: strsplit splits strings by separator [OK]

Common Mistakes:

• Confusing strsplit with paste or toupper functions
• Thinking strsplit counts characters
• Assuming strsplit joins strings

2. Which of the following is the correct syntax to split the string "apple,banana,orange" by commas using strsplit?

easy

A. strsplit("apple,banana,orange", " ")

B. strsplit("apple,banana,orange", ".")

C. strsplit("apple,banana,orange", ",")

D. strsplit("apple,banana,orange")

Solution

1. Step 1: Identify the separator in the string

   The string uses commas "," to separate words.

2. Step 2: Match the separator in strsplit syntax

   strsplit("apple,banana,orange", ",") uses "," as the separator, which is correct. strsplit("apple,banana,orange", ".") uses ".", C uses space, and D misses the separator argument.

3. Final Answer:

   strsplit("apple,banana,orange", ",") -> Option C

4. Quick Check:

   Separator matches comma = A [OK]

Hint: Use the exact separator character inside quotes [OK]

Common Mistakes:

• Forgetting to provide the separator argument
• Using wrong separator character
• Using unquoted separator

3. What is the output of the following R code?

result <- strsplit("one-two-three", "-")
print(result)

medium

A. [[1]] "one" "two" "three"

B. "one-two-three"

C. [1] "one" "two" "three"

D. Error: invalid separator

Solution

1. Step 1: Understand strsplit output type

   strsplit returns a list where each element is a character vector of split parts.

2. Step 2: Analyze the printed output

   The print shows a list with one element ([[1]]) containing the split strings "one", "two", "three".

3. Final Answer:

   [[1]] "one" "two" "three" -> Option A

4. Quick Check:

   strsplit returns list of vectors = A [OK]

Hint: Remember strsplit returns a list, not a vector directly [OK]

Common Mistakes:

• Expecting a simple vector instead of a list
• Confusing output with a single string
• Thinking strsplit throws an error for valid separator

4. Identify the error in this R code:

strsplit("cat,dog,bird", ",")[[2]]

medium

A. The string should be a vector, not a single string.

B. Index [[2]] is out of bounds because strsplit returns a list of length 1.

C. Missing parentheses around strsplit call.

D. Separator "," is incorrect for splitting.

Solution

1. Step 1: Check the output structure of strsplit

   strsplit returns a list with one element per input string. Here, input is one string, so list length is 1.

2. Step 2: Analyze the indexing [[2]]

   Trying to access [[2]] causes an out-of-bounds error because the list has only one element.

3. Final Answer:

   Index [[2]] is out of bounds because strsplit returns a list of length 1. -> Option B

4. Quick Check:

   List length 1, index 2 invalid = D [OK]

Hint: Check list length before using [[index]] [OK]

Common Mistakes:

• Assuming strsplit returns multiple list elements for one string
• Using wrong separator
• Misunderstanding list indexing

5. You have a vector of strings: c("red:blue", "green:yellow", "black:white"). How do you split each string by ":" and get a flat vector of all colors?

hard

A. unlist(strsplit(c("red:blue", "green:yellow", "black:white"), ":"))

B. strsplit(c("red:blue", "green:yellow", "black:white"), ":")

C. paste(strsplit(c("red:blue", "green:yellow", "black:white"), ":"))

D. split(c("red:blue", "green:yellow", "black:white"), ":")

Solution

1. Step 1: Use strsplit to split each string by ":"

   strsplit returns a list of character vectors for each element in the input vector.

2. Step 2: Flatten the list to a single vector

   Using unlist converts the list of vectors into one flat character vector containing all colors.

3. Final Answer:

   unlist(strsplit(c("red:blue", "green:yellow", "black:white"), ":")) -> Option A

4. Quick Check:

   Use unlist to flatten strsplit output = C [OK]

Hint: Use unlist() to flatten strsplit list output [OK]

Common Mistakes:

• Forgetting to unlist and getting a list instead of vector
• Using paste which concatenates instead of splitting
• Using split which is for factors, not strings