[R] tcl/tk return problem

[Prof Brian Ripley]

On Wed, 31 Aug 2005, Philippe Grosjean wrote:

> deggle wrote:
> > Hello,
> >
> > I'm very new in working with tcl/tk in R and have a problem which will
> > probably
> > sound silly to most of you.
> > Here is the code I have problems with:
> >
> > readcelfiles <- function()
> > {
> >    require(tcltk)
> >    tt <- tktoplevel()
> >    tkgrid(tklabel(tt,text="Choose a directory!"))
> >
> >  OnOK <- function()
> >  {
> >     fileDir<-tclvalue(tkchooseDirectory())
> >     data.raw <- ReadAffy(celfile.path=fileDir)
> >     #return(data.raw)
> >  }
> >
> >    OK.but <- tkbutton(tt,text="OK",command=OnOK)
> >    tkgrid(OK.but)
> >    tkfocus(tt)
> > }
> >
> > So after clicking on my "OK" button, I choose my directory and read the
> > cel-files.
> > But now I want to return the object to my workspace ... "return" doesn't
> > work here.
>
> I suppose you mean in the User Workspace. Your OnOK function should look
> like that:
>
> OnOK <- function() {
>       fileDir<-tclvalue(tkchooseDirectory())
>       data.raw <<- ReadAffy(celfile.path=fileDir)
> }
>
> Note that the function overwrites any existing 'data.raw', so this could
> be dangerous. Writting directly in the User Workspace is not advised
> from inside a function, but here, it is the simplest way to return a
> result from a tk widget action.

Maybe simplest, but not a very good way.  See
R_SOURCES/src/library/tcltk/R/utils.R for ideas on how to write a modal
dialog box that returns the value selected.

One problem with <<- is that it does not necessarily write in the
workspace.  You need

   assign("data.raw", ReadAffy(celfile.path=fileDir), envir=.GlobalEnv)

to be sure of that.  (The example code I quote does use <<- but in a
controlled way.)

-- 
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 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595