In my PREDICT 454 class, one of the R challenges that our professor wanted us to undertake involved creating a simple function that ‘acted’ like the venerable Magic 8 Ball. So let’s get to it!


  1. The function must output one of the following texts:
  • ‘I don’t see that happening.’
  • ‘You must be dreaming.’
  • ‘Chances are good.’
  • ‘If you work hard and stay focused, then this might happen.’
  • ‘When the sun shines, it shines on your face.’
  • ‘Definitely going to happen!’
  • ‘Take some time to think about it.’
  • ‘This is not a good idea!’
  • ‘This is a great idea!’
  • ‘Cannot be determined at this time. Try Again!’
  1. Add an optional feature in which the user can include the seed number

  2. The function should be called magic.8ball() and if a seed is to be used, then the function could called as magic.8ball(123)


Function Definition

magic.8ball <- function(x.seed) {
  # define messages
  msg1 <- "I don't see that happening."
  msg2 <- 'You must be dreaming.'
  msg3 <- 'Chances are good.'
  msg4 <- 'If you work hard and stay focused, then this might happen.'
  msg5 <- 'When the sun shines, it shines on your face.'
  msg6 <- 'Definitely going to happen!'
  msg7 <- 'Take some time to think about it.'
  msg8 <- 'This is not a good idea!'
  msg9 <- 'This is a great idea!'
  msg10 <- 'Cannot be determined at this time.  Try Again!'
  msg_list <- list(msg1, msg2, msg3, msg4, msg5, msg6, msg7, msg8, msg9, msg10)

  if(missing(x.seed)) {
    x <- sample(1:10,1)
  } else {
    x <- sample(1:10,1)

Function Results

Function with random seed

## [[1]]
## [1] "When the sun shines, it shines on your face."

Function with user-defined seed

## [[1]]
## [1] "Chances are good."

Function Explanation

For the most part, this function is quite simple. Although there are numerous ways to derive this solution, I felt it was easier to define each message into a variable and then store all of the variables in a list. Then, the function would simply sample an integer between 1 and 10 (since there are 10 messages) and recall the corresponding list member for display to the end user.

The slight twist in this example was the user-defined seed. In order ot do this correctly, I employed the command missing to check and see if the user had originally entered a value in the function call. If none is there, then the function uses a random seed and if the user did enter some number, then it sets the seed accordingly.

Hope all that makes sense. Let me know if you have any questions!