R help - Jun 2005 - locator() via tcltk

Hello,

I'm trying to write a function using tcltk to interactively modify a plot
and gather locator() data. I've read Peter's articles in Rnews, the help
pages in tcltk, http://bioinf.wehi.edu.au/~wettenhall/RTclTkExamples/,
plus a post in R-help sometime ago, but haven't found a solution.
The idea goes something like this:

require(tcltk)
testplot <- function() {
  getcoords <- function(...) {
    locator(5)
  }
  x <- 1:1000
  y <- rnorm(1000)
  plot(x, y)
  base <- tktoplevel()
  loc.pts <- tkbutton(base, text = "Get coordinates", command =
getcoords)
  quit.but <- tkbutton(base, text = "Quit",
                       command = function() tkdestroy(base))
  tkpack(loc.pts, quit.but)
}

I'd like testplot to return the value from getcoords. The "Get
coordinates" button seems to be correctly calling getcoords, and locator
is doing its job, but I don't know how to store its value. Any help is
very much appreciated.

Regards,
Sebastian
-- 
Sebastian P. Luque

Sebastian Luque wrote:
> Hello,
> 
> I'm trying to write a function using tcltk to interactively modify a
plot
> and gather locator() data. I've read Peter's articles in Rnews, the
help
> pages in tcltk, http://bioinf.wehi.edu.au/~wettenhall/RTclTkExamples/,
> plus a post in R-help sometime ago, but haven't found a solution.
> The idea goes something like this:
> 
> require(tcltk)
> testplot <- function() {
>   getcoords <- function(...) {
>     locator(5)
>   }
>   x <- 1:1000
>   y <- rnorm(1000)
>   plot(x, y)
>   base <- tktoplevel()
>   loc.pts <- tkbutton(base, text = "Get coordinates", command
= getcoords)
>   quit.but <- tkbutton(base, text = "Quit",
>                        command = function() tkdestroy(base))
>   tkpack(loc.pts, quit.but)
> }
> 
> I'd like testplot to return the value from getcoords. The "Get
> coordinates" button seems to be correctly calling getcoords, and
locator
> is doing its job, but I don't know how to store its value. Any help is
> very much appreciated.
You can do this with local functions.  For example,

  testplot <- function() {

    coords <- NA

    getcoords <- function(...) {
      coords <<- locator(5)
    }
    x <- 1:1000
    y <- rnorm(1000)
    plot(x, y)
    base <- tktoplevel()
    loc.pts <- tkbutton(base, text = "Get coordinates", command =
getcoords)
    quit.but <- tkbutton(base, text = "Quit",
                         command = function() tkdestroy(base))
    tkpack(loc.pts, quit.but)
    return(function() coords)
  }

This stores the results in a variable named coords in the testplot 
frame.  testplot itself returns a function that can read that value. 
You'd use it like this:

lastval <- testplot()

## do some button clicking...

lastval()   # will print the result of the last click.

This is one of the somewhat weird but very nice features of R.  S-PLUS 
doesn't work this way.

Duncan Murdoch

You have two asynchronous processes here: your R function will return, 
leaving a Tk widget up.  Duncan Murdoch's solution is to give you a 
function that will retrieve at some future stage the result of the last 
press (if any) of "Get coordinates" button.  Is that what you want?

I think it is more likely you want to wait for the Tk interaction and then 
return the results, that is use a `modal' widget.  If so, take a look at 
the examples in src/library/tcltk/R/utils.R which are modal and return 
their results.

On Fri, 3 Jun 2005, Sebastian Luque wrote:
> Hello,
>
> I'm trying to write a function using tcltk to interactively modify a
plot
> and gather locator() data. I've read Peter's articles in Rnews, the
help
> pages in tcltk, http://bioinf.wehi.edu.au/~wettenhall/RTclTkExamples/,
> plus a post in R-help sometime ago, but haven't found a solution.
> The idea goes something like this:
>
> require(tcltk)
> testplot <- function() {
>  getcoords <- function(...) {
>    locator(5)
>  }
>  x <- 1:1000
>  y <- rnorm(1000)
>  plot(x, y)
>  base <- tktoplevel()
>  loc.pts <- tkbutton(base, text = "Get coordinates", command =
getcoords)
>  quit.but <- tkbutton(base, text = "Quit",
>                       command = function() tkdestroy(base))
>  tkpack(loc.pts, quit.but)
> }
>
> I'd like testplot to return the value from getcoords. The "Get
> coordinates" button seems to be correctly calling getcoords, and
locator
> is doing its job, but I don't know how to store its value. Any help is
> very much appreciated.
-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595