Character (string) type in R Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this R code?

Consider the following R code snippet. What will it print?

R Programming

text <- "Hello, R!"
cat(substr(text, 8, 9))

A R!

B R

C R!\n

D lo

💡 Hint

Remember that substr extracts characters from start to end positions inclusive.

The substr function extracts characters from position 8 to 9. In "Hello, R!", position 8 is 'R' and position 9 is '!'. But cat prints without quotes and no newline by default, so it prints 'R!'. Option A is 'R' only, so the correct answer is A.

❓ Predict Output

intermediate

What does this R code print?

What is the output of this R code?

R Programming

text <- "Data123"
print(grepl("[0-9]", text))

A TRUE

B FALSE

C Error: invalid regular expression

D NA

💡 Hint

grepl returns TRUE if the pattern is found anywhere in the string.

The pattern "[0-9]" matches any digit. Since "Data123" contains digits, grepl returns TRUE.

🔧 Debug

advanced

Why does this R code produce an error?

This code is intended to concatenate two strings with a space. Why does it produce an error?

R Programming

str1 <- "Hello"
str2 <- 123
result <- paste(str1, str2, sep=" ")
print(result)

A Error because sep argument is invalid

B No error; output is "Hello 123"

C Error because str2 is numeric and paste requires strings

D Error because print cannot print numeric values

💡 Hint

Check how paste handles numeric arguments.

paste automatically converts numeric arguments to strings, so no error occurs. The output is "Hello 123".

❓ Predict Output

advanced

What is the output of this R code involving string splitting?

What does this R code print?

R Programming

text <- "apple,banana,carrot"
result <- strsplit(text, ",")[[1]]
print(length(result))

A 0

B 1

C Error: subscript out of bounds

D 3

💡 Hint

strsplit returns a list; extracting the first element gives the vector of split strings.

strsplit splits the string into c("apple", "banana", "carrot"), so length is 3.

🧠 Conceptual

expert

Which option correctly explains the behavior of R's character vectors?

Which statement about character vectors in R is TRUE?

A Character vectors automatically convert numbers to strings when combined.

B Character vectors store strings as linked lists internally.

C Character vectors are immutable; you cannot change individual characters inside a string element.

D Character vectors can contain elements of different types like numbers and strings.

💡 Hint

Think about how strings behave in R when you try to change a single character.

In R, strings inside character vectors are immutable; you cannot change a single character inside a string element directly.

Practice

1. What is the correct way to create a character string in R?

easy

A. Using quotes like "hello"

B. Using parentheses like (hello)

C. Using square brackets like [hello]

D. Using curly braces like {hello}

Solution

1. Step 1: Understand character string syntax in R

   Character strings must be enclosed in quotes, either single or double.

2. Step 2: Identify the correct option

   Only Using quotes like "hello" uses quotes correctly to create a character string.

3. Final Answer:

   Using quotes like "hello" -> Option A

4. Quick Check:

   Character strings = text inside quotes [OK]

Hint: Remember: text strings always go inside quotes [OK]

Common Mistakes:

• Using parentheses instead of quotes
• Forgetting to use quotes around text
• Using brackets or braces which are not for strings

2. Which of the following is the correct syntax to join two strings "Hello" and "World" in R?

easy

A. paste("Hello", "World")

B. join("Hello", "World")

C. concat("Hello", "World")

D. combine("Hello", "World")

Solution

1. Step 1: Recall string joining function in R

   In R, paste() is used to join strings with a space by default.

2. Step 2: Check the options

   Only paste("Hello", "World") uses the correct function paste() to join strings.

3. Final Answer:

   paste("Hello", "World") -> Option A

4. Quick Check:

   Use paste() to join strings [OK]

Hint: Use paste() to combine strings with spaces [OK]

Common Mistakes:

• Using non-existent functions like join or concat
• Forgetting quotes around strings
• Using functions that do not exist in base R

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

text <- "R is fun"
substr(text, 1, 3)

medium

A. "R is fun"

B. "R i"

C. "R is"

D. "is f"

Solution

1. Step 1: Understand substr() function

   substr(text, start, stop) extracts substring from position start to stop inclusive.

2. Step 2: Apply to given code

   Positions 1 to 3 in "R is fun" are "R", " ", and "i" which combine to "R i" but note the space is counted as a character.

3. Step 3: Check actual substring

   Positions 1 to 3 are characters: 'R' (1), ' ' (2), 'i' (3), so substring is "R i".

4. Final Answer:

   "R i" -> Option B

5. Quick Check:

   substr() extracts characters by position [OK]

Hint: Count characters including spaces for substr() [OK]

Common Mistakes:

• Ignoring spaces as characters
• Confusing substr() with substring() behavior
• Off-by-one errors in positions

4. Identify the error in this R code that tries to create a character vector:

words <- c(hello, "world", "R")

medium

A. Extra comma after hello

B. Using c() instead of paste()

C. Wrong function name, should be concat()

D. Missing quotes around hello

Solution

1. Step 1: Check each element in the vector

   All elements must be character strings with quotes, but hello is unquoted.

2. Step 2: Identify the error

   Missing quotes around hello causes R to look for a variable named hello, which likely does not exist.

3. Final Answer:

   Missing quotes around hello -> Option D

4. Quick Check:

   Character strings need quotes [OK]

Hint: Always quote text inside c() for character vectors [OK]

Common Mistakes:

• Forgetting quotes around text
• Confusing c() with paste() for vectors
• Assuming c() concatenates strings without quotes

5. You have a vector of words c("apple", "banana", "cherry"). How do you create a single character string with these words separated by commas and a space, like "apple, banana, cherry"?

hard

A. paste0(c("apple", "banana", "cherry"), collapse=",")

B. paste(c("apple", "banana", "cherry"), sep=",")

C. paste(c("apple", "banana", "cherry"), collapse=", ")

D. paste0(c("apple", "banana", "cherry"), sep=",")

Solution

1. Step 1: Understand paste() with collapse

   The collapse argument joins vector elements into one string separated by the given string.

2. Step 2: Check the options

   paste(c("apple", "banana", "cherry"), collapse=", ") correctly uses paste() with collapse=", " to join words with comma and space.

3. Step 3: Why not sep?

   sep controls separator between arguments, not vector elements; collapse is needed here.

4. Final Answer:

   paste(c("apple", "banana", "cherry"), collapse=", ") -> Option C

5. Quick Check:

   Use collapse to join vector elements [OK]

Hint: Use collapse in paste() to join vector elements [OK]

Common Mistakes:

• Using sep instead of collapse
• Using paste0 which does not add separators
• Not quoting the separator string