Return values in R Programming - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to return the sum of two numbers.

R Programming

add_numbers <- function(a, b) {
  return([1])
}

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

Aa * b

Ba - b

Ca + b

Da / b

Attempts:

3 left

💡 Hint

Common Mistakes

Using subtraction (-) instead of addition (+).

Forgetting to use return() to send back the result.

The function should return the sum of a and b. Using a + b correctly adds the two numbers.

2fill in blank

medium

Complete the code to return the first element of a vector.

R Programming

get_first <- function(vec) {
  return(vec[1])
}

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

A[[2]]

B[1]

C[[1]]

D[2]

Attempts:

3 left

💡 Hint

Common Mistakes

Using double square brackets ([[1]]) which is for lists, not vectors.

Using index 2 instead of 1.

In R, to get the first element of a vector, use single square brackets with index 1: vec[1].

3fill in blank

hard

Fix the error in the function to return the length of a vector.

R Programming

vector_length <- function(x) {
  len <- length(x)
  return([1])
}

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

Ax

Bx.length

Clength

Dlen

Attempts:

3 left

💡 Hint

Common Mistakes

Returning the vector x instead of its length.

Trying to return length which is a function, not a variable.

The variable len stores the length of x. The function should return len.

4fill in blank

hard

Fill both blanks to return a named list with the vector and its mean.

R Programming

summary_stats <- function(data) {
  result <- list([1] = data, [2] = mean(data))
  return(result)
}

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

Avalues

Baverage

Cmean

Ddata

Attempts:

3 left

💡 Hint

Common Mistakes

Using the same name for both list elements.

Using incorrect or unclear names.

The list should have names values for the data vector and average for its mean.

5fill in blank

hard

Fill all three blanks to return a list with the sum, product, and difference of two numbers.

R Programming

calculate <- function(x, y) {
  result <- list([1] = x + y, [2] = x * y, [3] = x - y)
  return(result)
}

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

Asum

Bproduct

Cdifference

Dtotal

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up the names and operations.

Using generic names like total instead of specific ones.

The list should have names sum, product, and difference for the respective calculations.

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