[R] tcl/tk return problem

[Duncan Murdoch]

On 8/31/2005 8:57 AM, Prof Brian Ripley wrote:
> On Wed, 31 Aug 2005, Duncan Murdoch wrote:
> 
>> Prof Brian Ripley wrote:
>> > 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.)
>>
>> This works, and you weren't suggesting it as a good style, but I'd like
>> to say it's really a bad style to write to .GlobalEnv.
> 
> It was the question asked! 

Yes, I agree, but I was pointing out that it is probably the wrong question.

Duncan Murdoch

 > If you use a non-modal tcltk dialog you
> have little choice, as the parent function will have returned and vanished
> long ago.  Now, having a widget firing off R commands independently of the
> command line is not a great idea (R's evaluator is not multithreaded and
> this could be interspersed in another computation) so there is a lot to be
> said for using dialog boxes modally.
> 
>> The controlled use of <<- as in tk_select.list from the file you
>> quoted is really the best way to solve this problem.  As a general
>> rule, you shouldn't stomp on something you don't own, and functions
>> don't own variables in .GlobalEnv.
> 
> One could argue the user who pressed the button does: it is the user
> workspace.
> 
>> What tk_select.list does is define OnOK locally, and use <<- to write to
>> the tk_select.list environment.  Then the result can be manipulated and
>> returned politely, without stomping on anything anywhere.
>