R programming function without ()

问题

So, I Have the following very simple map.r file.

I'm trying to have the user type "click" in interactive mode and then have the function .

Since it's a function, the user has to type "click()" how can I make it so that they only have to the word (w/o parentheses), and then have that function do something with the img.

So the user types:

mydist("image.pnm")

click

//And then the function click does what it's supposed to

mydist <- function(mapfile) {

    img <- read.pnm(mapfile)

    plot(img)
}

click <- function() {

    //Prompt user to click on img
}

回答1:

If you give it a class of its own and a print method which echoes that message you can achieve your goal.

  print.click <- function(x, ...){
    #
    # could do something here
    # the <something> could be a plot or calculation
    plot(1:10, 10:1, type="l")
   cat("Your click message here\n perhaps \n Downward line plotted!")
     invisible(x)
 }
 click <- "click"
 class(click) <- "click"


 click
# Your click message here
# perhaps 
# Downward line plotted!

Even if you wanted to "encapsulate" the class definition in the object itself as Aaron demonstrated, you would not be limited to printing a message. You could do something like this:

print.click <- function(x, ...) {plot(1:10, 10:1, type="l")
   cat("prompt user to click on img...\n")

If you wanted to call locator, you could extend the interactivity with the user.

回答2:

Here's the 'proper' way to do it. This is an example from my .Rprofile file.

invisible(makeActiveBinding("newq", function(...){quartz();par(cex=.75); cat("OK\n")}, .GlobalEnv))

The function makeActiveBinding does some sort of magic so the complete function gets called w/o need for any parentheses.

回答3:

Here's one way to do what you've asked for. However, there may be a better way to do what you're trying to do.

click <- structure(1, class="click")
print.click <- function(x, ...) {
  cat("prompt user to click on img...\n")
}

Then

> click
prompt user to click on img...

回答4:

I could be totally confused as to what you want to do, but I think something like below may answer your query. It can be expanded upon by adding other 'else-if' options and other custom functions to be run as a result of whatever the user types.

customfunction <- function() {
print(1:10)
}

mydist <- function(mapfile) {

   img <- read.pnm(mapfile)
   plot(img)

ANSWER <- readline("")

# customfunction() will be run (printing 1:10) as soon as 
# the user types "click" and hits enter

if (ANSWER=="click") customfunction()

}

来源：https://stackoverflow.com/questions/8130469/r-programming-function-without

标签

function

interactive