recursion function r

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

Explanation:

1. The function r is defined to take one parameter, n.
2. Inside the function, there is an if statement to check if n is less than or equal to 0.
3. If the condition is true, the function returns 1. This is the base case for the recursion.
4. If the condition is false (i.e., n is greater than 0), the function calculates the factorial of n using recursion.
5. It calls itself with the argument n - 1 and multiplies the result by n.
6. The recursion continues until the base case is reached (when n becomes 0 or negative).
7. The final result is the product of all the numbers from n down to 1, which is the factorial of the original input n.