Function arguments in R Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of function with default and named arguments

What is the output of this R code?

R Programming

f <- function(x, y = 2) {
  x + y
}

result <- f(y = 3, x = 4)
print(result)

A Error: unused argument (y = 3)

B [1] 5

C [1] 7

D [1] 6

💡 Hint

Remember that named arguments can be passed in any order.

The function f adds x and y. The call f(y=3, x=4) assigns x=4 and y=3, so the result is 4 + 3 = 7. But the default y=2 is overridden by y=3. The sum is 7.

❓ Predict Output

intermediate

Effect of missing argument with default

What will this R code print?

R Programming

g <- function(a, b = 10) {
  a * b
}

print(g(5))

A [1] 50

B Error: argument "b" is missing, with no default

C [1] 15

D [1] 5

💡 Hint

Check the default value of b.

The function multiplies a by b. Since b has a default value of 10 and is not provided, it uses 10. So 5 * 10 = 50.

🔧 Debug

advanced

Identify the error in function argument usage

What error does this R code produce?

R Programming

h <- function(x, y) {
  x + y
}

h(3)

A Error in h(3) : unused argument (3)

B Error in h(3) : argument "y" is missing, with no default

C Error in h(3) : object 'y' not found

D No error, output is 3

💡 Hint

Check if all required arguments are provided.

The function h requires two arguments x and y. Calling h(3) provides only x, so R raises an error about missing argument y.

❓ Predict Output

advanced

Output with ... (ellipsis) argument

What does this R code print?

R Programming

k <- function(x, ...) {
  args <- list(...)
  sum <- x
  for (val in args) {
    sum <- sum + val
  }
  sum
}

print(k(1, 2, 3, 4))

A [1] 10

B [1] 24

C [1] 1

D Error: object 'val' not found

💡 Hint

The ... collects extra arguments as a list.

The function sums x plus all values passed in ... . Here, x=1 and ... = 2,3,4. Sum is 1+2+3+4=10.

🧠 Conceptual

expert

Number of arguments in a function call

How many arguments are passed to the function call below?

R Programming

m <- function(a, b = 2, c = 3) {
  a + b + c
}

m(1, c = 4)

A Error: missing argument

B 3

C 1

D 2

💡 Hint

Count only arguments explicitly passed in the call.

The call m(1, c=4) passes two arguments: a=1 (positional) and c=4 (named). b uses default 2. So 2 arguments are passed.

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