Question

In the below function, I would like to control the input so that if any value but the first three choices (any value that does not equal 1-3) are entered the function will loop back to the original question.

T<-function(){
Load<-readline("
Choose Task 
1 Task 1
2 Task 2
3 Task 3 ")
for(i in 1:10){
    if(Load=="")
    {print.noquote("No Value Entered"); Load<-readline("
Choose Task 
1 Task 1
2 Task 2
3 Task 3 ")
    }else
    if(Load==1)
    {source("/Users/JD/Desktop/R1.R")}
    else
    if(Load==2)
    {source("/Users/JD/Desktop/R2.R",print.eval=TRUE)}
    else
    if(Load==3)
    {source("/Users/JD/Desktop/R3.R",print.eval=TRUE)}
    else
    {print.noquote("Must enter 1-3"); ** loop back to "Choose Task"**}



}}

So where I have the ** would be a line looping back to the second line of the code. I’ve already controlled for a “blank” response, but I would like to do something similar for anything not equaling 1-3. If looping back is not allowed, perhaps there may be a different way to get the same effect.

Answer 1

You can use a combination of switch and recursion

ChooseTask <- function() {
    Load <- readline("Choose Task. 1, 2, or 3: ")
    switch(Load, 
           "1"={cat("1", "\n")},
           "2"={cat("2", "\n")},
           "3"={cat("3", "\n")},
            {
                print.noquote("Must enter 1-3") 
                ChooseTask()
            })
}
> ChooseTask()
Choose Task. 1, 2, or 3: 2
2 
> ChooseTask()
Choose Task. 1, 2, or 3: 5
[1] Must enter 1-3
Choose Task. 1, 2, or 3: 1
1