user input in R (Rscript and Widows command prompt)

Question

I am trying to figure out, how can i run an r script, using Rscript in windows command prompt and ask for user input.

So far, i have found answers on how do ask for user input in R's interactive shell. Any effort in doing the same with readline() or scan() has failed.

example:

I have a polynomial y=cX where X can take more than one values X1,X2,X3 and so on. C variable is know, so what i need in order to calculate the value of y is to ask the user for the Xi values and store them somewhere inside my script.

Uinput <- function() {
    message(prompt"Enter X1 value here: ")
    x <- readLines()
}

Is this the way to go? Any additional arguments? Will as.numeric help? How do i return X1? And will the implementation differ depending on the OS?

Thanks.

score 4 · Answer 1 · answered Apr 06 '14 at 19:51

4

That's the general way to go, but the implementation needs some work: you don't want readLines, you want readline (yes, the name is similar. Yes, this is dumb. R is filled with silly things ;).

What you want is something like:

UIinput <- function(){

    #Ask for user input
    x <- readline(prompt = "Enter X1 value: ")

    #Return
    return(x)
}

You probably want to do some error-handling there, though (I could provide an X1 value of FALSE, or "turnip"), and some type conversion, since readline returns a one-entry character vector: any numeric input provided should probably be converted to, well, a numeric input. So a nice, user-proof way of doing this might be...

UIinput <- function(){

    #Ask for user input
    x <- readline(prompt = "Enter X1 value: ")

    #Can it be converted?
    x <- as.numeric(x)

    #If it can't, be have a problem
    if(is.na(x)){

         stop("The X1 value provided is not valid. Please provide a number.")

    }

    #If it can be, return - you could turn the if into an if/else to make it more
    #readable, but it wouldn't make a difference in functionality since stop()
    #means that if the if-condition is met, return(x) will never actually be
    #evaluated.
    return(x)
}

answered Apr 06 '14 at 19:51

1

The only problem is that even though code seems to run smoothly and without errors, nothing happens in terminal. Literally nothing.. – Apr 07 '14 at 06:11
That's...strange. I assume you're actually calling the function? – Apr 07 '14 at 16:39
Alright i found the answer i was looking for elsewhere. Thanks for the effort nonetheless – Apr 08 '14 at 07:35
1

@KapelNick don't leave us hanging - how did you resolve it? :). – Apr 08 '14 at 12:16
2

`cat("blablabla: ") x <- readLines(con="stdin", 1) x <- as.numeric(x)` worked for me – Apr 09 '14 at 06:32
1

That'd work, but I'm confused as to why the above solution didn't. How were you running it? – Apr 09 '14 at 16:14
Well i did try several variations of the code without any success. Did it work for you? I might be going trying to implement it again in the future and see why it didn't work. For the time being my schedule is tight. – Apr 10 '14 at 08:03
I believe the solution user347128 works if you put curly brackets around the calls: `{ username <- UIinput() password <-UIinput() }` – Reddspark May 15 '18 at 18:49

score 0 · Answer 2 · answered Jul 02 '22 at 14:53

0

This did not work for me running a Rscript via Rscript.exe in a batch file (.bat). As someone wrote it this worked for me as well :

cat("blablabla: ")
x <- readLines(con="stdin", 1)
x <- as.numeric(x)

answered Jul 02 '22 at 14:53

Dorian Grv

421
5
9

user input in R (Rscript and Widows command prompt)

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