Chapter 7. Programs

In this chapter, you will build a real, working slot machine that you can play by running an R function. When you’re finished, you’ll be able to play it like this:

play()
## 0 0 DD
## $0

play()
## 7 7 7
## $80

The play function will need to do two things. First, it will need to randomly generate three symbols; and, second, it will need to calculate a prize based on those symbols.

The first step is easy to simulate. You can randomly generate three symbols with the sample function—just like you randomly “rolled” two dice in Part I. The following function generates three symbols from a group of common slot machine symbols: diamonds (DD), sevens (7), triple bars (BBB), double bars (BB), single bars (B), cherries (C), and zeroes (0). The symbols are selected randomly, and each symbol appears with a different probability:

get_symbols <- function() {
  wheel <- c("DD", "7", "BBB", "BB", "B", "C", "0")
  sample(wheel, size = 3, replace = TRUE,
    prob = c(0.03, 0.03, 0.06, 0.1, 0.25, 0.01, 0.52))
}

You can use get_symbols to generate the symbols used in your slot machine:

get_symbols()
## "BBB" "0"   "C"

get_symbols()
## "0" "0" "0"

get_symbols()
## "7" "0" "B"

get_symbols uses the probabilities observed in a group of video lottery terminals from Manitoba, Canada. These slot machines became briefly controversial in the 1990s, when a reporter decided to test their payout rate. The machines appeared to pay out only 40 cents on the dollar, even though the manufacturer claimed they would ...

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