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

Recall & Review

beginner

How do you run a single line of R code in the R console?

You type the line of code and press Enter. The R console then executes the code and shows the result.

beginner

What is the purpose of the source() function in R?

The source() function runs all the R code saved in a file. It helps you run scripts instead of typing code line by line.

beginner

What happens when you run print("Hello, world!") in R?

R shows the text Hello, world! in the console. The print() function displays the message on the screen.

beginner

How can you run multiple lines of R code at once in RStudio?

You select the lines you want to run and press Ctrl+Enter (Cmd+Enter on Mac). This sends the selected code to the console to run together.

beginner

What is the difference between running code in the R console and running code in an R script file?

Running code in the console executes one line at a time immediately. Running code in a script file lets you save many lines and run them all at once or in parts.

Which function runs all the R code saved in a file?

A source()

B run()

C execute()

D load()

The source() function runs all the R code saved in a file.

How do you run selected lines of code in RStudio?

A Press Ctrl+S

B Press Ctrl+Enter (Cmd+Enter on Mac)

C Press Ctrl+R

D Press Ctrl+C

Selecting lines and pressing Ctrl+Enter (Cmd+Enter on Mac) runs the selected code in RStudio.

What does the print() function do in R?

A Stops the program

B Saves the code to a file

C Runs a script file

D Displays output in the console

The print() function shows the given message or value in the console.

What happens when you press Enter after typing code in the R console?

A The code is saved but not run

B The console clears

C The code runs and shows the result

D The program exits

Pressing Enter runs the typed code immediately and shows the output.

Which is true about running code in an R script file?

A You can run many lines at once

B You can only run one line at a time

C It does not show output

D It only works in the console

An R script file lets you save and run many lines of code together.

Explain how to run R code using the console and using a script file.

Think about immediate execution vs saved scripts.

Describe how you can run multiple lines of code at once in RStudio.

Focus on keyboard shortcuts and selection.

Practice

1. What does running R code mean?

easy

A. Installing R software

B. Only writing comments in the script

C. Saving files without executing them

D. Typing commands or running script files to perform tasks

Solution

1. Step 1: Understand the meaning of running code

   Running code means executing commands or scripts to perform actions in R.

2. Step 2: Identify the correct description

   Typing commands or running script files matches the definition of running R code.

3. Final Answer:

   Typing commands or running script files to perform tasks -> Option D

4. Quick Check:

   Running code = executing commands/scripts [OK]

Hint: Running code means executing commands or scripts [OK]

Common Mistakes:

• Confusing running code with just writing comments
• Thinking saving files runs code
• Mixing running code with installing software

2. Which of the following is the correct way to run an R script named script.R from the console?

easy

A. source('script.R')

B. run('script.R')

C. execute('script.R')

D. load('script.R')

Solution

1. Step 1: Recall the function to run scripts in R

   The function source() is used to run R scripts from the console.

2. Step 2: Match the correct syntax

   source('script.R') correctly runs the script named script.R.

3. Final Answer:

   source('script.R') -> Option A

4. Quick Check:

   Run script = source() [OK]

Hint: Use source() to run R scripts from console [OK]

Common Mistakes:

• Using run() which is not an R function
• Using execute() which does not exist in R
• Using load() which loads data, not scripts

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

print(2 + 3 * 4)

medium

A. 14

B. 20

C. 24

D. Error

Solution

1. Step 1: Understand operator precedence in R

   Multiplication (*) has higher precedence than addition (+), so 3 * 4 is calculated first.

2. Step 2: Calculate the expression

   3 * 4 = 12, then 2 + 12 = 14.

3. Final Answer:

   14 -> Option A

4. Quick Check:

   2 + (3 * 4) = 14 [OK]

Hint: Multiply before adding in R expressions [OK]

Common Mistakes:

• Adding before multiplying ignoring precedence
• Expecting error due to syntax
• Confusing multiplication with addition

4. Identify the error in the following R code snippet:

print('Hello World)

medium

A. Missing closing parenthesis for print

B. Missing closing quote for the string

C. print() is not a valid function in R

D. No error, code runs fine

Solution

1. Step 1: Check string syntax

   The string starts with a single quote but does not have a matching closing quote.

2. Step 2: Confirm the error type

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

3. Final Answer:

   Missing closing quote for the string -> Option B

4. Quick Check:

   Unclosed string = syntax error [OK]

Hint: Always close quotes around strings [OK]

Common Mistakes:

• Thinking print() is invalid in R
• Ignoring missing quote and blaming parentheses
• Assuming code runs without errors

5. You want to run multiple R commands stored in a file named analysis.R. Which is the best way to run all commands at once and see their output in the console?

hard

A. Open the file and run each line manually

B. Copy and paste the file content into the console line by line

C. Use source('analysis.R') to run the whole script

D. Restart R and open the file without running it

Solution

1. Step 1: Understand how to run multiple commands in R

   Running a whole script at once is done using the source() function.

2. Step 2: Identify the best method for running all commands and seeing output

   source('analysis.R') runs all commands in the file and shows output in the console.

3. Final Answer:

   Use source('analysis.R') to run the whole script -> Option C

4. Quick Check:

   Run script = source() [OK]

Hint: Use source() to run entire R scripts at once [OK]

Common Mistakes:

• Running lines manually wastes time
• Copy-pasting line by line is inefficient
• Restarting R does not run code automatically