Inline R code in R Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of inline R code in a string

What is the output of this R code when run?

R Programming

name <- "Alice"
result <- paste0("Hello, `r name`!")
print(result)

A "Hello, `r name`!"

B "Hello, Alice!"

C Error: object 'name' not found

D "Hello, NULL!"

💡 Hint

Inline R code inside strings with backticks is not evaluated automatically in base R.

In base R, backticks with `r` inside strings are not evaluated. The string remains as is.

❓ Predict Output

intermediate

Evaluating inline R code with glue package

What is the output of this R code?

R Programming

library(glue)
name <- "Bob"
result <- glue("Hello, {name}!")
print(result)

A "Hello, {name}!"

B Error: object 'name' not found

C "Hello, Bob!"

D "Hello, NULL!"

💡 Hint

The glue package evaluates expressions inside curly braces {}.

The glue function evaluates {name} and replaces it with the value of the variable name.

❓ Predict Output

advanced

Output of inline R code in R Markdown chunk

In an R Markdown document, what will this inline R code produce when rendered? `r 2 + 3 * 4`

A Error: object not found

B 14

C 20

D 2 + 3 * 4

💡 Hint

Inline R code in R Markdown evaluates the expression and inserts the result.

The expression 2 + 3 * 4 evaluates as 2 + 12 = 14.

❓ Predict Output

advanced

Error from incorrect inline R code syntax

What error does this R code produce? `r if(TRUE) print("Yes") else print("No")`

A NULL

B "Yes"

C "No"

D Error: unexpected 'else' in "else"

💡 Hint

Inline R code expects a single expression, not a full if-else statement.

The inline code syntax does not allow multi-line or compound statements like if-else without braces.

🧠 Conceptual

expert

How inline R code is processed in R Markdown

Which statement best describes how inline R code (e.g., `r expression`) is processed in an R Markdown document?

A The expression inside `r` is evaluated during knitting and its result replaces the inline code in the output.

B The inline code is treated as plain text and appears unchanged in the output document.

C The expression is evaluated only when the document is opened in RStudio, not during knitting.

D The inline code is executed in a separate R session after the document is rendered.

💡 Hint

Think about when the R Markdown document is converted to output formats.

During knitting, R Markdown evaluates inline R code and inserts the results into the output document.

Practice

1. What is the purpose of using inline R code with `r expression` in documents?

easy

A. To comment out code in R scripts

B. To insert the result of an R expression directly into the text

C. To create a new R function

D. To define a variable in R

Solution

1. Step 1: Understand inline R code usage

   Inline R code uses backticks and r to embed R expressions inside text.

2. Step 2: Identify the purpose

   This allows the result of the R expression to appear directly in the document text, making it dynamic.

3. Final Answer:

   To insert the result of an R expression directly into the text -> Option B

4. Quick Check:

   Inline R code = insert R result in text [OK]

Hint: Inline code shows R results inside text using backticks [OK]

Common Mistakes:

• Thinking inline code defines variables
• Confusing inline code with comments
• Believing inline code creates functions

2. Which of the following is the correct syntax for inline R code to show the sum of 2 and 3?

easy

A. `r 2 + 3`

B. `r sum(2 + 3`

C. `r sum 2, 3`

D. `r sum(2,3`

Solution

1. Step 1: Inline R code evaluates expressions

   Inline R code executes the R expression between the backticks and inserts its result (here, 2+3=5).

2. Step 2: Check each option's validity

   `r sum 2, 3` missing parens around args: sum 2 -> sum(2)=2, then ,3 -> 3 (wrong).
   `r sum(2 + 3` missing ) -> syntax error.
   `r 2 + 3` -> 5 (correct).
   `r sum(2,3` missing ) -> syntax error.

3. Final Answer:

   `r 2 + 3` -> Option A

4. Quick Check:

   Simple expression inside `r` is best [OK]

Hint: Use simple expressions inside `r` for inline code [OK]

Common Mistakes:

• Adding extra parentheses inside sum()
• Using incorrect commas or spaces
• Confusing function call syntax

3. What will be the output of this inline R code snippet in a document? `r paste('Hello', 'World')`

medium

A. Error

B. paste('Hello', 'World')

C. HelloWorld

D. Hello World

Solution

1. Step 1: Understand paste() function

   The paste() function joins strings with a space by default, so paste('Hello', 'World') returns "Hello World".

2. Step 2: Inline code outputs the result

   The inline R code evaluates the expression and inserts the result "Hello World" into the document.

3. Final Answer:

   Hello World -> Option D

4. Quick Check:

   paste() joins strings with space [OK]

Hint: paste() joins words with space by default [OK]

Common Mistakes:

• Expecting no space between words
• Thinking inline code shows code, not result
• Confusing paste() with paste0()

4. Identify the error in this inline R code: `r mean(c(1, 2, '3'))`

medium

A. Missing closing backtick

B. mean() cannot take vectors

C. Character '3' causes mean() to fail

D. No error, code runs fine

Solution

1. Step 1: Check vector contents

   The vector c(1, 2, '3') mixes numbers and a character, so R converts all to character.

2. Step 2: mean() expects numeric input

   mean() cannot calculate mean of characters, so it will produce an error.

3. Final Answer:

   Character '3' causes mean() to fail -> Option C

4. Quick Check:

   mean() needs numeric vector [OK]

Hint: mean() needs numeric values, no characters [OK]

Common Mistakes:

• Ignoring type conversion in vectors
• Assuming mean() works on mixed types
• Missing quotes around characters

5. You want to display the number of rows in a data frame df inline in your report. Which inline R code correctly shows this count?

hard

A. `r nrow(df)`

B. `r length(df)`

C. `r df$nrow`

D. `r count(df)`

Solution

1. Step 1: Recall function to get row count

   The function nrow() returns the number of rows in a data frame.

2. Step 2: Check each option

   `r nrow(df)` uses nrow(df) which is correct. `r length(df)` uses length(df) which returns number of columns, not rows. `r df$nrow` tries to access a non-existent column nrow. `r count(df)` uses count() which is not a base R function for this purpose.

3. Final Answer:

   `r nrow(df)` -> Option A

4. Quick Check:

   nrow() gives row count [OK]

Hint: Use nrow() to get rows count inline [OK]

Common Mistakes:

• Using length() for rows instead of columns
• Trying to access nrow as a column
• Using non-base functions without loading packages