Wait for a user input for 5 seconds and use a default value otherwise

Question

I would like to give the user an opportunity to enter an input, and use a default value if they do not enter anything after 5 seconds.

Here's for the input part:

input <- readline(prompt="Do something? (y/n): ")

Is there a way to do it in R?

Drava

?Sys.sleep maybe? – Stancil

Humm, the way I understand it, Sys.sleep can make R wait, but it will not force R to stop waiting and carry on the execution if nobody answers.. – Drava

This may be hard, "Furthermore, it is not possible to interrupt/break out of a "readline" prompt (e.g. readline() and readLines()) using timeouts; the timeout exception will not be thrown until after the user completes the prompt (i.e. after pressing ENTER)." You will have to be creative..rdocumentation.org/packages/R.utils/versions/2.7.0/topics/… – Literatim

Not sure if you want to keep this text based, but this can be done with tcltk2 using tclAfter – Alarice

It looks to me that @Literatim is right, and even tcltk2::tclAfter is like Sys.sleep and only allows to delay the execution of a function, not to force R to carry on the execution of a function after waiting a few seconds. – Drava

Answer 1

Here is how I accomplish a window prompt allowing the user to select the number of threads to start in a cluster. It uses a default value and then it will proceed after the OK button is pressed or 5 seconds pass.

library(tcltk2)

clusterCount = 1

tklist <- list()
tklist <- within(tklist, {
  # define processor input window
  win1 <- tktoplevel()
  rb1 <- tk2radiobutton(win1)
  rb2 <- tk2radiobutton(win1)
  rb3 <- tk2radiobutton(win1)
  rb4 <- tk2radiobutton(win1)
  rbCluster <- tclVar(clusterCount)
  tkconfigure(rb1, text = "one",  variable = rbCluster, value = 1L)
  tkconfigure(rb2, text = "two",  variable = rbCluster, value = 2L)
  tkconfigure(rb3, text = "three", variable = rbCluster, value = 3L)
  tkconfigure(rb4, text = "four", variable = rbCluster, value = 4L)
  onOK <- function() {
    clusterCount <<- as.integer(tclvalue(rbCluster))
    tkdestroy(win1)
  }
  butOK <- tk2button(win1, text = "OK", width = -8, command = onOK)

  # geometry manager
  tkgrid(tk2label(win1, text = "how many cores?"), padx = 10, pady = c(15, 5))
  tkgrid(rb1, padx = 10, pady = c(0, 5))
  tkgrid(rb2, padx = 10, pady = c(0, 15))
  tkgrid(rb3, padx = 10, pady = c(0, 15))
  tkgrid(rb4, padx = 10, pady = c(0, 15))
  tkgrid(butOK, padx = 10, pady = c(5, 15))
  tclAfter(5000, function() tkdestroy(win1)) # delay for prompt and then close window to proceed
  tkfocus(win1)
  tkwait.window(win1)
})

After the window closes then clusterCount will either remain the default 1 or can be changed to 2, 3, or 4.

Alarice

Answer 2

If you have a newer version of R then you can try withTimeout function from the utils package, to wrap the readline function.

There is a difficult to use function in base R called setTimeLimit.

My buggy attempt at a solution follows This worked in RGui, but it also seemed to reliably crash R-studio

timed_readline <- function(prompt = '',default,timeout = 10)
{
    inner <- function(timeout)    # wrapped in internal function to stop error being displayed
    {
        setTimeLimit(elapsed=timeout,transient=TRUE)
        a <- readline('')
        setTimeLimit(transient=TRUE)
        return(a)
    }

    cat(prompt)
    b <- default
    try({b <- inner(timeout)},silent=TRUE) 
    return(b)
}

As such I can't recommend this code but it might inspire you to something workable

Berck

thanks for taking the time Aaron, much appreciated. this approach seems to works fine with any other function, but not with readline() unfortunately. – Drava

Answer 3

I can't find the way to skip that interaction in console. Anyway I'm leaving a function concerning time where, if you push enter out of time in order to skip the promt, you will get a predefined value. I hope it is a way to save that console interaction.

#set time in seconds to get an answer from prompt 
#some interaction in console is needed, sorry

Q <- function (x) {
    t0 <- Sys.time() 
    input <- readline(prompt="Do something? (y/n): ")
    tf <- Sys.time()-t0

    if (tf > x){
        input <- "your predefined answer"
    }

    print (tf) #remove if you like
    return (input)
}

Q(5)

Felicitous