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rsampledo.callset-difference

Monty Hall In R - setdiff unexpected results

I am writing a program in R to do some simulations of the Monty Hall Problem explained here, https://www.youtube.com/watch?v=4Lb-6rxZxx0

Consider this code, sample(setdiff(doors, c(pick, car)),1) "should" be 3 every time, but it isn't.

doors <- 1:3
pick <- 2
car <- 1
sample(setdiff(doors, c(pick, car)),1)
[1] 3
sample(setdiff(doors, c(pick, car)),1)
[1] 1

Any idea where I am going wrong?

Thank you.

Solution

  • Your issue is that you end up calling sample.int since

    doors <- 3L
pick <- sample(doors, 1)
car <- sample(doors, 1)
class(setdiff(doors, c(pick, car)))
#R [1] "integer"

    and 

    length(setdiff(doors, c(pick, car)))
#R [1] 1

    See help("sample.int") or 

    body(sample)
#R {
#R    if (length(x) == 1L && is.numeric(x) && is.finite(x) && x >= 
#R         1) {
#R         if (missing(size)) 
#R            size <- x
#R         sample.int(x, size, replace, prob)
#R     }
#R    else {
#R        ...

    There is no point in sampling unless you have more than one variable in your set.