Return values in R Programming - Mini Project: Build & Apply

Return values

📖 Scenario: Imagine you are creating a simple calculator function in R that adds two numbers and returns the result. This is like using a vending machine: you put in money (input), press a button (function), and get a snack (output). Here, the snack is the sum of two numbers.

🎯 Goal: You will build a function called add_numbers that takes two numbers as input and returns their sum. Then, you will call this function and print the result.

📋 What You'll Learn

Create a function called add_numbers with two parameters: a and b

Inside the function, return the sum of a and b

Call the function with the numbers 5 and 7 and store the result in a variable called result

Print the value of result

💡 Why This Matters

🌍 Real World

Functions that return values are used everywhere in programming to perform calculations, process data, and give back results. For example, a shopping app might use functions to calculate total prices.

💼 Career

Understanding how to write functions that return values is a key skill for any programming job, enabling you to write reusable and organized code.

1

Create the function add_numbers

Write a function called add_numbers that takes two parameters named a and b. For now, leave the function body empty.

R Programming

add_numbers <- function(a, b) {
  # Your code here
}

Hint

Use the syntax function(parameter1, parameter2) { } to create a function in R.

2

Add the return statement

Inside the add_numbers function, write a line that returns the sum of a and b using the return() function.

R Programming

add_numbers <- function(a, b) {
  # Your code here
}

Hint

Use return(a + b) to send back the sum from the function.

3

Call the function and store the result

Call the function add_numbers with the numbers 5 and 7. Store the returned value in a variable called result.

R Programming

add_numbers <- function(a, b) {
  return(a + b)
}

# Your code here

Hint

Use result <- add_numbers(5, 7) to call the function and save the output.

4

Print the result

Write a line to print the value of the variable result.

R Programming

add_numbers <- function(a, b) {
  return(a + b)
}

result <- add_numbers(5, 7)

# Your code here

Hint

Use print(result) to display the sum.

Practice

1. What does the return() function do in an R function?

easy

A. It sends a value back to where the function was called.

B. It prints a message on the screen.

C. It stops the entire program immediately.

D. It creates a new variable inside the function.

Solution

1. Step 1: Understand the purpose of return()

   The return() function is used inside an R function to send a value back to the place where the function was called.

2. Step 2: Differentiate from other actions

   Printing messages or stopping the program are different actions and not the role of return().

3. Final Answer:

   It sends a value back to where the function was called. -> Option A

4. Quick Check:

   Return sends value back = A [OK]

Hint: Return sends output back from function to caller [OK]

Common Mistakes:

• Thinking return prints output
• Confusing return with stopping program
• Assuming return creates variables

2. Which of the following is the correct way to return the value 10 from a function in R?

easy

A. return 10

B. return(10)

C. return{10}

D. return <- 10

Solution

1. Step 1: Recall correct return syntax in R

   In R, the correct syntax to return a value is to use return() with parentheses around the value.

2. Step 2: Check each option

   return(10) uses return(10), which is correct. Others have syntax errors or wrong usage.

3. Final Answer:

   return(10) -> Option B

4. Quick Check:

   Use parentheses with return = A [OK]

Hint: Use parentheses with return to send value back [OK]

Common Mistakes:

• Omitting parentheses after return
• Using curly braces instead of parentheses
• Assigning return as a variable

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

my_func <- function() {
  x <- 5
  y <- 10
  x + y
}
result <- my_func()
print(result)

medium

A. NULL

B. 5

C. Error

D. 15

Solution

1. Step 1: Understand function return behavior without explicit return()

   In R, if no return() is used, the last evaluated expression is returned automatically. Here, x + y is the last expression.

2. Step 2: Calculate the last expression value

   x = 5 and y = 10, so x + y equals 15. This value is returned and stored in result.

3. Final Answer:

   15 -> Option D

4. Quick Check:

   Last expression returned = 15 [OK]

Hint: Last expression in function returns automatically if no return() [OK]

Common Mistakes:

• Expecting NULL if no return()
• Thinking print inside function returns value
• Confusing variable assignment with return

4. Identify the error in this R function that tries to return the sum of two numbers:

add_numbers <- function(a, b) {
  sum <- a + b
  return sum
}

medium

A. Variable sum is not defined

B. Function should not use return

C. Missing parentheses after return

D. Function parameters are incorrect

Solution

1. Step 1: Check return statement syntax

   The return statement in R requires parentheses around the value to return. Here, return sum is missing parentheses.

2. Step 2: Confirm variable and parameters are correct

   The variable sum is defined as a + b, and parameters are correct. So no error there.

3. Final Answer:

   Missing parentheses after return -> Option C

4. Quick Check:

   return() needs parentheses = B [OK]

Hint: Always use parentheses with return in R [OK]

Common Mistakes:

• Omitting parentheses after return
• Confusing variable scope errors
• Thinking return is optional always

5. You want to write an R function that returns a named list with two values: the sum and product of two numbers. Which code correctly returns both values?

hard

A. calc <- function(a, b) {
return(list(sum = a + b, product = a * b))
}

B. calc <- function(a, b) {
sum <- a + b
product <- a * b
return(sum, product)
}

C. calc <- function(a, b) {
sum <- a + b
product <- a * b
return c(sum, product)
}

D. calc <- function(a, b) {
sum <- a + b
product <- a * b
list(sum, product)
}

Solution

1. Step 1: Understand how to return multiple values in R

   R functions can return a list to send back multiple values together.

2. Step 2: Check each option for correct syntax

   calc <- function(a, b) { return(list(sum = a + b, product = a * b)) } correctly returns a named list with sum and product. calc <- function(a, b) { sum <- a + b product <- a * b return(sum, product) } tries to return two values separately, which is invalid. calc <- function(a, b) { sum <- a + b product <- a * b return c(sum, product) } returns a vector instead of a list. calc <- function(a, b) { sum <- a + b product <- a * b list(sum, product) } returns a list but without return(), so it returns the last expression implicitly, which works but does not name elements.

3. Final Answer:

   calc <- function(a, b) { return(list(sum = a + b, product = a * b)) } -> Option A

4. Quick Check:

   Return named list for multiple values = C [OK]

Hint: Use return(list(...)) to send multiple values back [OK]

Common Mistakes:

• Trying to return multiple values without list
• Using return with multiple arguments incorrectly
• Forgetting to name list elements