Inline R code in R Programming - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is inline R code in R Markdown?

Inline R code lets you run R commands directly inside text. It shows the result right in the sentence when you knit the document.

beginner

How do you write inline R code in R Markdown?

Use a single backtick, then r, then your R code, and close with a backtick. Like this: `r 2 + 2`.

beginner

What will this inline R code output? `r paste('Hello', 'World')`

It will output: Hello World inside the text where the code is placed.

intermediate

Why use inline R code instead of writing results manually?

Inline R code keeps your document up-to-date automatically. If data or calculations change, the output updates when you knit again.

intermediate

Can inline R code include complex expressions or just simple values?

Inline R code can include any R expression, from simple numbers to complex functions, as long as it returns a value to show.

How do you write inline R code in R Markdown?

A `r your_code`

B ```r your_code ```

C <r>your_code</r>

D {{r your_code}}

Inline R code uses a single backtick, then r, then the code, and closes with a backtick.

What does inline R code do when you knit an R Markdown document?

A Deletes the code from the document

B Shows the code but does not run it

C Runs the code but hides the result

D Runs the code and shows the result inside the text

Inline R code runs and shows the result directly in the text output.

Which of these is a valid inline R code example?

A `r mean(c(1,2,3))`

B ```r mean(c(1,2,3))```

C <r>mean(c(1,2,3))</r>

D {{mean(c(1,2,3))}}

Only option D uses the correct inline R code syntax.

What happens if the inline R code contains an error?

A The code is ignored and no output is shown

B The knitting process stops with an error message

C The code runs but shows a blank space

D The document knits but shows the code as text

Errors in inline R code cause knitting to stop and show an error.

Why is inline R code useful in reports?

A It makes the document run faster

B It hides all code from the reader

C It updates results automatically when data changes

D It formats text with colors

Inline R code keeps results current by running code each time you knit.

Explain how to use inline R code in an R Markdown document and why it is helpful.

Think about how you mix code and text in one sentence.

Describe a situation where inline R code would save you time compared to writing results manually.

Imagine you have a report with numbers that change often.

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