Recursive functions in R Programming - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a recursive function?

A recursive function is a function that calls itself to solve smaller parts of a problem until it reaches a simple case it can solve directly.

beginner

What is the base case in recursion?

The base case is the simplest situation in a recursive function where the function stops calling itself to avoid infinite loops.

intermediate

How does recursion relate to breaking down problems?

Recursion breaks a big problem into smaller, similar problems, solves each smaller problem, and combines the results to solve the original problem.

intermediate

What happens if a recursive function has no base case?

Without a base case, the function keeps calling itself forever, causing a stack overflow error or program crash.

beginner

Example: What does this R function do?

factorial <- function(n) {
  if (n == 0) return(1)
  else return(n * factorial(n - 1))
}

This function calculates the factorial of a number n by multiplying n by the factorial of n-1 until it reaches 0.

What is the purpose of the base case in a recursive function?

A To stop the recursion and prevent infinite calls

B To call the function again

C To make the function run faster

D To print the result

The base case stops the recursion by providing a simple answer, preventing infinite calls.

In R, how does a recursive function call itself?

A By using its own name inside the function

B By using a loop

C By calling another function

D By using a variable

A recursive function calls itself by using its own name inside its definition.

What will happen if a recursive function lacks a base case?

A It will return zero

B It will run forever and cause an error

C It will run once and stop

D It will print a message

Without a base case, recursion never stops, causing a stack overflow error.

Which problem is a good fit for recursion?

A Reading a file

B Adding two numbers

C Printing a message once

D Calculating factorial of a number

Factorial calculation naturally breaks down into smaller factorial problems, perfect for recursion.

What does this R code return?

factorial(3)

A 9

B 3

C 6

D 1

factorial(3) = 3 * factorial(2) = 3 * 2 * factorial(1) = 3 * 2 * 1 = 6.

Explain how a recursive function works using a real-life example.

Think about how you might solve a big task by doing smaller similar tasks first.

Describe why a base case is important in recursive functions.

What happens if the function never stops calling itself?