Function arguments in R Programming - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a function argument in R?

A function argument is a value you give to a function when you call it. It tells the function what data to work with.

beginner

How do you define a function with arguments in R?

You write the function name, then inside parentheses list the argument names. For example: myfun <- function(x, y) { x + y } defines a function with two arguments, x and y.

intermediate

What happens if you call a function without providing all its arguments?

If the function has default values for some arguments, those defaults are used. Otherwise, R will give an error saying an argument is missing.

intermediate

What is a default argument value in R functions?

A default argument value is a value assigned to an argument in the function definition. If you don’t provide that argument when calling the function, R uses the default.

beginner

How can you pass arguments to a function by name in R?

You can specify the argument name when calling the function, like myfun(y = 5, x = 3). This lets you give arguments in any order.

What will happen if you call sum(1, 2) in R?

A It returns 2

B It returns 3

C It returns 1

D It returns an error

The sum function adds the numbers 1 and 2 and returns 3.

How do you set a default value for an argument in an R function?

A By assigning a value in the function definition, like <code>function(x = 5)</code>

B By calling the function with no arguments

C By using the <code>default()</code> function

D By writing <code>setdefault(x)</code>

You assign a default value directly in the function definition.

What is the correct way to call a function with named arguments in R?

A <code>myfun(x = 2, y = 3)</code>

B <code>myfun(2, 3)</code>

C <code>myfun(, x = 2, y = 3)</code>

D <code>myfun(x:2, y:3)</code>

Named arguments use the syntax name = value inside the function call.

If a function argument has a default value, what happens when you omit it in the call?

A An error occurs

B The function ignores the argument

C The argument becomes NULL

D The default value is used

R uses the default value if you don’t provide that argument.

Which of these is NOT a valid way to pass arguments to a function in R?

A By position, like <code>fun(1, 2)</code>

B By name, like <code>fun(y = 2, x = 1)</code>

C By using <code>fun(x:1, y:2)</code>

D By mixing named and positional arguments

The syntax x:1 is not valid for passing arguments in R.

Explain how function arguments work in R and how default values affect function calls.

Think about what happens when you call a function with fewer arguments than defined.

Describe how to use named arguments in R function calls and why they might be helpful.

Consider how naming arguments can make your code easier to read and less error-prone.

Practice

1. What is the purpose of function arguments in R?
my_function <- function(x, y) { x + y }

easy

A. To create variables outside the function

B. To print output from the function

C. To send information into the function for processing

D. To stop the function from running

Solution

1. Step 1: Understand what arguments do

   Arguments are values you give to a function so it can use them inside its code.

2. Step 2: Look at the example function

   The function takes x and y as inputs and adds them, showing arguments are inputs.

3. Final Answer:

   To send information into the function for processing -> Option C

4. Quick Check:

   Function arguments = inputs [OK]

Hint: Arguments are inputs you give to functions [OK]

Common Mistakes:

• Thinking arguments print output
• Confusing arguments with variables outside
• Believing arguments stop function execution

2. Which of the following is the correct way to define a function with two arguments a and b in R?

easy

A. my_func <- function {a, b} return(a + b)

B. my_func <- function(a, b) { return(a + b) }

C. my_func <- function[a, b] { return(a + b) }

D. my_func <- function(a; b) { return(a + b) }

Solution

1. Step 1: Recall R function syntax

   Functions use parentheses () to list arguments separated by commas.

2. Step 2: Check each option

   Only my_func <- function(a, b) { return(a + b) } uses parentheses and commas correctly; others use wrong brackets or separators.

3. Final Answer:

   my_func <- function(a, b) { return(a + b) } -> Option B

4. Quick Check:

   Function args use (a, b) [OK]

Hint: Use parentheses and commas for arguments [OK]

Common Mistakes:

• Using square brackets instead of parentheses
• Separating arguments with semicolons
• Omitting parentheses around arguments

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

add <- function(x, y = 5) {
  x + y
}
add(3)

medium

A. 8

B. 3

C. 5

D. Error: missing argument y

Solution

1. Step 1: Understand default argument values

   The function add has y defaulting to 5 if not provided.

2. Step 2: Call the function with one argument

   Calling add(3) uses x=3 and default y=5, so result is 3 + 5 = 8.

3. Final Answer:

   8 -> Option A

4. Quick Check:

   3 + default 5 = 8 [OK]

Hint: Default arguments fill in missing values [OK]

Common Mistakes:

• Expecting error when argument is missing
• Ignoring default argument values
• Confusing which argument has default

4. Identify the error in this R function definition:

multiply <- function(x, y) {
  result <- x * z
  return(result)
}

medium

A. Function should not use return statement

B. Function name cannot be multiply

C. Arguments must have default values

D. Variable z is not defined inside the function

Solution

1. Step 1: Check variables used inside function

   The function uses z but only x and y are arguments; z is undefined.

2. Step 2: Understand variable scope

   Variables inside functions must be defined or passed as arguments; z is missing.

3. Final Answer:

   Variable z is not defined inside the function -> Option D

4. Quick Check:

   Undefined variable = error [OK]

Hint: Use only defined arguments or variables inside functions [OK]

Common Mistakes:

• Using variables not passed as arguments
• Thinking return is optional error
• Believing arguments must have defaults

5. You want to create a function greet that takes a name and an optional greeting message (default "Hello"). Which function definition is correct to achieve this?

hard

A. greet <- function(name, message = "Hello") { paste(message, name) }

B. greet <- function(name = "Hello", message) { paste(message, name) }

C. greet <- function(name, message) { paste(message, name) }

D. greet <- function(message = "Hello", name) { paste(name, message) }

Solution

1. Step 1: Identify default argument placement

   In R, arguments with defaults must come after those without defaults.

2. Step 2: Check each option

   greet <- function(name, message = "Hello") { paste(message, name) } correctly places message with default after name without default and uses paste correctly.

3. Final Answer:

   greet <- function(name, message = "Hello") { paste(message, name) } -> Option A

4. Quick Check:

   Default args last = correct [OK]

Hint: Put default arguments after required ones [OK]

Common Mistakes:

• Placing default arguments before required ones
• Forgetting default values
• Mixing argument order in paste function