Code chunks and output in R Programming - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print the number 5.

R Programming

print([1])

Drag options to blanks, or click blank then click option'

Afive

Bx

C"5"

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Putting quotes around 5 prints it as text, not number.

Using a variable name without defining it causes an error.

The print() function outputs the value inside the parentheses. Using 5 prints the number 5.

2fill in blank

medium

Complete the code to assign the value 10 to variable x.

R Programming

[1] <- 10

Drag options to blanks, or click blank then click option'

Ay

Bx

C10

Dprint(x)

Attempts:

3 left

💡 Hint

Common Mistakes

Using the value 10 on the left side instead of variable name.

Using print instead of variable name causes syntax error.

In R, the assignment operator <- assigns the value on the right to the variable on the left. Here, x is the variable name.

3fill in blank

hard

Fix the error in the code to calculate the sum of 3 and 4.

R Programming

result <- 3 [1] 4

Drag options to blanks, or click blank then click option'

A+

B-

C*

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using minus or other operators changes the result.

Leaving the operator blank causes syntax error.

The plus sign + adds two numbers. Using it here sums 3 and 4 correctly.

4fill in blank

hard

Fill both blanks to create a vector of numbers from 1 to 5.

R Programming

numbers <- c([1]:[2])

Drag options to blanks, or click blank then click option'

A1

Bc

C5

Dseq

Attempts:

3 left

💡 Hint

Common Mistakes

Using function names instead of numbers inside the colon.

Swapping the numbers changes the sequence.

The colon operator : creates a sequence from the first number to the second. Here, 1:5 makes numbers 1 through 5.

5fill in blank

hard

Fill all three blanks to create a named vector with scores greater than 50.

R Programming

scores <- c(Alice=60, Bob=45, Carol=75)
passed <- scores[scores [1] [2]]
result <- [3](names(passed))

Drag options to blanks, or click blank then click option'

A>

B50

Csort

Dmean

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong comparison operators like < or =.

Using mean() instead of sort() for names.

This code selects scores greater than 50 using > and 50. Then it gets the names of those who passed and sorts them with sort().

Practice

1. What is the purpose of an R code chunk in an R Markdown document?

easy

A. To run R code and show its output inline with text

B. To write plain text without any code

C. To create a table of contents automatically

D. To add images to the document

Solution

1. Step 1: Understand R Markdown structure

   R Markdown uses code chunks to embed R code inside text documents.

2. Step 2: Purpose of code chunks

   Code chunks run R code and display results inline, mixing code and output.

3. Final Answer:

   To run R code and show its output inline with text -> Option A

4. Quick Check:

   Code chunk = run code + show output [OK]

Hint: Code chunks run code and show output together [OK]

Common Mistakes:

• Thinking code chunks only hold text
• Confusing code chunks with document sections
• Assuming code chunks add images automatically

2. Which of the following is the correct way to start an R code chunk in R Markdown?

easy

A. {r}```

B. ```r

C. ```{r}

D. {r}

Solution

1. Step 1: Recall R Markdown chunk syntax

   R code chunks start with three backticks followed by {r} exactly.

2. Step 2: Check each option

   Only ```{r} correctly starts a chunk; others are invalid syntax.

3. Final Answer:

   ```{r} -> Option C

4. Quick Check:

   Chunk start = ```{r} [OK]

Hint: Start chunks with three backticks and {r} [OK]

Common Mistakes:

• Omitting curly braces around r
• Using only two backticks
• Confusing HTML tags with chunk syntax

3. What will be the output of this R code chunk?

```{r}
x <- 5
x * 2
```

medium

A. [1] 10

B. 10

C. x * 2

D. Error: object 'x' not found

Solution

1. Step 1: Understand the code execution

   Variable x is assigned 5, then multiplied by 2, resulting in 10.

2. Step 2: R output format

   R prints numeric output with index [1] before the value.

3. Final Answer:

   [1] 10 -> Option A

4. Quick Check:

   5 * 2 = 10 with [1] prefix [OK]

Hint: R prints numeric output with [1] prefix [OK]

Common Mistakes:

• Ignoring the [1] prefix in output
• Expecting just '10' without index
• Thinking code prints the expression itself

4. Identify the error in this R code chunk:

```{r}
print("Hello)
```

medium

A. Missing closing curly brace for chunk

B. Missing closing quote in the string

C. Incorrect function name 'print'

D. No error, code runs fine

Solution

1. Step 1: Check the string syntax

   The string starts with a double quote but lacks the closing double quote.

2. Step 2: Consequence of missing quote

   This causes a syntax error because the string is not properly closed.

3. Final Answer:

   Missing closing quote in the string -> Option B

4. Quick Check:

   Unclosed string causes syntax error [OK]

Hint: Check all quotes are closed in strings [OK]

Common Mistakes:

• Assuming chunk braces cause error
• Thinking print is misspelled
• Ignoring missing quote errors

5. You want to run an R code chunk but hide the code and only show the output. Which chunk option should you use?

hard

A. ```{r, include=FALSE}

B. ```{r, eval=FALSE}

C. ```{r, message=FALSE}

D. ```{r, echo=FALSE}

Solution

1. Step 1: Understand chunk options

   echo=FALSE hides the code but runs it, showing output only.

2. Step 2: Compare other options

   eval=FALSE skips running code, include=FALSE hides both code and output, message=FALSE hides messages only.

3. Final Answer:

   ```{r, echo=FALSE} -> Option D

4. Quick Check:

   echo=FALSE hides code, shows output [OK]

Hint: Use echo=FALSE to hide code but show output [OK]

Common Mistakes:

• Using eval=FALSE hides output too
• Using include=FALSE hides everything
• Confusing message=FALSE with code hiding