Default argument values in R Programming - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a function with a default argument value.

R Programming

greet <- function(name = [1]) {
  paste("Hello", name)
}

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

A"World"

BWorld

Cname

D"name"

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to put quotes around the default string value.

Using a variable name without quotes as default.

The default value for the argument name should be a string, so it must be enclosed in quotes.

2fill in blank

medium

Complete the code to call the function without providing the argument, so it uses the default value.

R Programming

greet([1])

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

A"Alice"

B(no argument)

Cname = "Alice"

Dname

Attempts:

3 left

💡 Hint

Common Mistakes

Passing an empty string instead of no argument.

Trying to pass the argument name without a value.

Calling the function without any argument uses the default value.

3fill in blank

hard

Fix the error in the function definition by completing the default argument value correctly.

R Programming

multiply <- function(x, y = [1]) {
  x * y
}

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

A2

B"2"

Cy

Dx

Attempts:

3 left

💡 Hint

Common Mistakes

Using quotes around numbers for default numeric arguments.

Using variable names as default values.

The default value should be a number, not a string or variable name.

4fill in blank

hard

Fill both blanks to create a function with two default arguments and return their sum.

R Programming

add <- function(a = [1], b = [2]) {
  a + b
}

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

A1

B0

C2

D"0"

Attempts:

3 left

💡 Hint

Common Mistakes

Using strings instead of numbers for default values.

Using the same value for both defaults.

The function has two default numeric arguments: a defaults to 0 and b defaults to 2.

5fill in blank

hard

Fill all three blanks to define a function with default arguments and call it with one argument.

R Programming

power <- function(base = [1], exponent = [2]) {
  base ^ exponent
}

result <- power([3])
result

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

A2

B3

C5

Dbase = 5

Attempts:

3 left

💡 Hint

Common Mistakes

Passing argument with name when only value is needed.

Mixing up base and exponent values.

The function defaults to base=2 and exponent=3. Calling power(5) sets base=5 and uses default exponent=3.

Practice

1. What happens if you call an R function with a default argument but do not provide that argument?

easy

A. The function asks the user to input the missing argument.

B. The function returns an error because the argument is missing.

C. The function uses the default value specified in the function definition.

D. The function ignores the argument and runs without it.

Solution

1. Step 1: Understand default arguments in R

   Default arguments provide a preset value if no value is given when calling the function.

2. Step 2: Behavior when argument is missing

   If the argument is not provided, R uses the default value automatically without error.

3. Final Answer:

   The function uses the default value specified in the function definition. -> Option C

4. Quick Check:

   Missing argument uses default value [OK]

Hint: If argument missing, default value is used automatically [OK]

Common Mistakes:

• Thinking missing argument causes error
• Assuming function asks for input
• Believing function ignores missing argument silently

2. Which of the following is the correct way to define a function in R with a default argument x set to 10?

easy

A. myfunc <- function(x <- 10) { return(x) }

B. myfunc <- function(x = 10) { return(x) }

C. myfunc <- function(x: 10) { return(x) }

D. myfunc <- function(x == 10) { return(x) }

Solution

1. Step 1: Recall R function default argument syntax

   In R, default values are assigned with = inside the function definition.

2. Step 2: Check each option

   Only myfunc <- function(x = 10) { return(x) } uses x = 10 correctly. Others use invalid syntax like :, <-, or ==.

3. Final Answer:

   myfunc <- function(x = 10) { return(x) } -> Option B

4. Quick Check:

   Default argument uses = in function definition [OK]

Hint: Use = to assign default values in function arguments [OK]

Common Mistakes:

• Using <- or : instead of = for default values
• Using == which is a comparison, not assignment
• Placing default outside function parentheses

3. What is the output of this R code?

add <- function(a, b = 5) {
  return(a + b)
}
add(3)

medium

A. 8

B. 3

C. Error: argument 'b' missing

D. 5

Solution

1. Step 1: Identify default argument usage

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

2. Step 2: Call function with only a=3

   Since b is missing, it uses default 5, so result is 3 + 5 = 8.

3. Final Answer:

   8 -> Option A

4. Quick Check:

   3 + default 5 = 8 [OK]

Hint: If argument missing, default value is used [OK]

Common Mistakes:

• Expecting error for missing argument
• Ignoring default and using only provided argument
• Confusing output with just the first argument

4. Consider this R function:

multiply <- function(x, y = 2) {
  x * y
}
multiply(4, )

What is the problem with this code?

medium

A. Function returns 8 because y defaults to 2.

B. Function throws error because x is missing.

C. Function ignores y and multiplies by 1.

D. Syntax error due to trailing comma without value.

Solution

1. Step 1: Analyze function call syntax

   The call multiply(4, ) has a comma but no second argument value, which is invalid syntax in R.

2. Step 2: Understand R argument rules

   Trailing commas without values cause syntax errors; you must omit the comma if skipping optional arguments.

3. Final Answer:

   Syntax error due to trailing comma without value. -> Option D

4. Quick Check:

   Trailing comma without value causes syntax error [OK]

Hint: No trailing commas without values in function calls [OK]

Common Mistakes:

• Assuming default used despite syntax error
• Thinking function returns result ignoring syntax
• Confusing missing argument with missing value

5. You want to write an R function greet that prints a greeting message. It should take a name argument with default "Guest" and a punctuation argument with default "!". Which function definition correctly implements this?

hard

A. greet <- function(name = "Guest", punctuation = "!") { paste0("Hello, ", name, punctuation) }

B. greet <- function(name, punctuation) { paste0("Hello, ", name = "Guest", punctuation = "!") }

C. greet <- function(name = Guest, punctuation = !) { paste0("Hello, ", name, punctuation) }

D. greet <- function(name = "Guest", punctuation) { paste0("Hello, ", name, punctuation = "!") }

Solution

1. Step 1: Check default argument syntax

   Defaults must be assigned inside the function definition using = and quoted strings for text.

2. Step 2: Validate each option

   greet <- function(name = "Guest", punctuation = "!") { paste0("Hello, ", name, punctuation) } correctly sets defaults with quotes and uses them in paste0. Other options misuse default assignment by placing it inside the function body, omitting defaults for optional arguments, or lacking quotes around strings (e.g., name = Guest, punctuation = !).

3. Final Answer:

   greet <- function(name = "Guest", punctuation = "!") { paste0("Hello, ", name, punctuation) } -> Option A

4. Quick Check:

   Default arguments set with = and quoted strings [OK]

Hint: Set defaults inside function parentheses with = and quotes for text [OK]

Common Mistakes:

• Assigning defaults inside function body
• Forgetting quotes around string defaults
• Omitting default for all optional arguments