Return values in R Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this R function call?

Consider the following R function and its call. What value does it return?

R Programming

multiply_and_add <- function(x, y) {
  result <- x * y
  return(result + 5)
}
multiply_and_add(3, 4)

A 17

B 7

C 12

D 15

💡 Hint

Remember the function multiplies x and y first, then adds 5 before returning.

The function multiplies 3 and 4 to get 12, then adds 5, so the return value is 17.

❓ Predict Output

intermediate

What does this R function return when called?

Look at this R function and its call. What is the returned value?

R Programming

check_even <- function(num) {
  if (num %% 2 == 0) {
    return(TRUE)
  } else {
    return(FALSE)
  }
}
check_even(7)

A TRUE

B NULL

C 7

D FALSE

💡 Hint

The function returns TRUE if the number is even, otherwise FALSE.

7 is not even, so the function returns FALSE.

❓ Predict Output

advanced

What is the output of this nested return function?

Analyze the following R code. What value does the function return when called with input 5?

R Programming

nested_return <- function(x) {
  inner <- function(y) {
    return(y * 2)
  }
  return(inner(x) + 3)
}
nested_return(5)

A 10

B 13

C 15

D 8

💡 Hint

The inner function doubles the input, then the outer adds 3.

inner(5) returns 10, then adding 3 gives 13.

❓ Predict Output

advanced

What does this function return when no explicit return is used?

What is the output of this R function call?

R Programming

no_return <- function(x) {
  y <- x + 2
  y * 3
}
no_return(4)

A NULL

B 6

C 18

D 12

💡 Hint

In R, the last evaluated expression is returned if no return() is used.

x=4, y=6, last expression y*3 = 18 is returned.

❓ Predict Output

expert

What is the output of this recursive function call?

Consider this recursive R function. What value does factorial(4) return?

R Programming

factorial <- function(n) {
  if (n == 1) {
    return(1)
  } else {
    return(n * factorial(n - 1))
  }
}
factorial(4)

A 24

B 10

C 16

D 1

💡 Hint

Factorial multiplies n by factorial of n-1 until n is 1.

factorial(4) = 4 * 3 * 2 * 1 = 24.

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