Question

Let’s imagine you would like to construct a simple test based on the condition setdiff(input, 1:9).

How can I construct an

if isnotempty(setdiff(input, 1:9)) stop ("not valid") 

statement which stops execution when input is c(3, 12) but continues when input is c(2,5,7) say?
Many thanks,
Bertie

Answer 1

You could use ?length:

isEmpty <- function(x) {
    return(length(x)==0)
}

input <- c(3, 12);

if (!isEmpty(setdiff(input, 1:9))) {
    stop ("not valid")
}