Function arguments in R Programming - Mini Project: Build & Apply

Function arguments

📖 Scenario: You are helping a small bakery calculate the total cost of different types of cakes ordered by customers. Each cake has a price and a quantity ordered.

🎯 Goal: Build a function that takes the price and quantity of a cake as arguments and returns the total cost. Then use this function to calculate the total cost for a specific order.

📋 What You'll Learn

Create a function called calculate_cost that takes two arguments: price and quantity.

Inside the function, multiply price by quantity and return the result.

Call the function with price = 15 and quantity = 3.

Print the result of the function call.

💡 Why This Matters

🌍 Real World

Calculating costs based on quantity and price is common in shops, restaurants, and online stores.

💼 Career

Understanding how to write functions with arguments is essential for automating calculations and processing data efficiently in many programming jobs.

1

Create the function skeleton

Write a function called calculate_cost that takes two arguments: price and quantity. For now, leave the function body empty.

R Programming

calculate_cost <- function(price, quantity) {
  # Your code here
}

Hint

Use the function keyword to define a function with two arguments.

2

Add the calculation inside the function

Inside the calculate_cost function, multiply price by quantity and return the result using the return() function.

R Programming

calculate_cost <- function(price, quantity) {
  # Multiply price and quantity and return the result
  # Your code here
}

Hint

Use return(price * quantity) to send back the total cost.

3

Call the function with specific values

Call the calculate_cost function with price = 15 and quantity = 3, and save the result in a variable called total.

R Programming

calculate_cost <- function(price, quantity) {
  return(price * quantity)
}

# Call the function and save the result
# Your code here

Hint

Use total <- calculate_cost(15, 3) to call the function and store the result.

4

Print the total cost

Print the value of the variable total to show the total cost.

R Programming

calculate_cost <- function(price, quantity) {
  return(price * quantity)
}

total <- calculate_cost(15, 3)

# Print the total cost
# Your code here

Hint

Use print(total) to display the total cost.

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