R help - Jul 2008 - tklistbox and extracting selection to R

Dear experts,

   I am trying to understand why is it that when I paste (into the R console)
the following code to select an option from a list:

  require(tcltk)
  tt<-tktoplevel()
 
tl<-tklistbox(tt,height=ntx,selectmode="single",background="white")
  tkgrid(tklabel(tt,text="Select the legend of" ))
  tkgrid(tl)
  treatments<<-levels.tx
  for(i in (1:ntx))
  {
      tkinsert(tl,"end",treatments[i])
  }

  OnOK<-function()
  {
      tx.choice1<<-treatments[as.integer(tkcurselection(tl))+1]
      tkdestroy(tt)
        
  }
  OK.but<-tkbutton(tt,text="    OK    ", command=OnOK)
  tkgrid(OK.but)

tx.choice1


     the console can't find tx.choice1, but if I type tx.choice1 directly
into the console, it returns the value I selected from the list.

   I am running R 2.7.1, OS: linnux, I run R within emacs.

Thank you very much for you help,

Judith

The <<- assignment can be very tricky and Tk windows have their own world.
If you just copy and paste the below (with ntx and levels.tx defined, it would
have been nice to have the example fully self running), then the OnOk function
has been defined and linked to the button, but never run, so when it looks for
tx.choice1, it has not been defined yet.  But after you make a selection and
click on ok, then it has.  I prefer to do this type of thing fully in a function
(keep all the varibles defined in a local environment), then return the result. 
Something like:

getlegend <- function(treatments){
  if(!require(tcltk)) stop('need tcltk')

  ntx <- length(treatments)
  tx.choice1 <- ''

  tt<-tktoplevel()
 
tl<-tklistbox(tt,height=ntx,selectmode="single",background="white")
  tkgrid(tklabel(tt,text="Select the legend of" ))
  tkgrid(tl)

  for(i in (1:ntx))
  {
      tkinsert(tl,"end",treatments[i])
  }

  OnOK<-function()
  {
      tx.choice1<<-treatments[as.integer(tkcurselection(tl))+1]
      tkdestroy(tt)

  }
  OK.but<-tkbutton(tt,text="    OK    ", command=OnOK)
  tkgrid(OK.but)

  tkwait.window(tt)
  return(tx.choice1)
}

Then you can run the getlegend function like:
> getlegend( levels(state.division) )
And it will wait until you select something and click on OK, then return the
selection (which the user can save or do whatever they want with).

Hope this helps,

--
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at imail.org
(801) 408-8111


> -----Original Message-----
> From: r-help-bounces at r-project.org
> [mailto:r-help-bounces at r-project.org] On Behalf Of Judith Flores
> Sent: Tuesday, July 22, 2008 10:41 AM
> To: RHelp
> Subject: [R] tklistbox and extracting selection to R
>
> Dear experts,
>
>    I am trying to understand why is it that when I paste
> (into the R console) the following code to select an option
> from a list:
>
>   require(tcltk)
>   tt<-tktoplevel()
>  
tl<-tklistbox(tt,height=ntx,selectmode="single",background="white")
>   tkgrid(tklabel(tt,text="Select the legend of" ))
>   tkgrid(tl)
>   treatments<<-levels.tx
>   for(i in (1:ntx))
>   {
>       tkinsert(tl,"end",treatments[i])
>   }
>
>   OnOK<-function()
>   {
>       tx.choice1<<-treatments[as.integer(tkcurselection(tl))+1]
>       tkdestroy(tt)
>
>   }
>   OK.but<-tkbutton(tt,text="    OK    ", command=OnOK)
>   tkgrid(OK.but)
>
> tx.choice1
>
>
>      the console can't find tx.choice1, but if I type
> tx.choice1 directly into the console, it returns the value I
> selected from the list.
>
>    I am running R 2.7.1, OS: linnux, I run R within emacs.
>
> Thank you very much for you help,
>
> Judith
>
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