[R] monitor variable change

[Rainer M Krug]

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On 02/16/2011 03:29 PM, Hadley Wickham wrote:
> One way to implement this functionality is with a task manager callback:
> 
> watch <- function(varname) {
>   old <- get(varname)
> 
>   changed <- function(...) {
>     new <- get(varname)
>     if (!identical(old, new)) {
>       message(varname, " is now ", new)
>       old <<- new
>     }
>     TRUE
>   }
>   invisible(addTaskCallback(changed))
> }
> 
> a <- 1
> watch("a")
> a <- 2

Wow - I was looking for something like that for a long time - this is
absolutely perfect for debugging. I guess I will use it quite often.

Thanks,

Rainer


> 
> 
> Hadley
> 
> On Wed, Feb 16, 2011 at 9:38 AM, Alaios <alaios at yahoo.com> wrote:
>> Dear all I would like to ask you if there is a way in R to monitor in R when a value changes.
>>
>> Right now I use the sprintf('my variables is %d \n, j) to print the value of the variable.
>>
>> Is it possible when a 'big' for loop executes to open in a new window to dynamically check only the variable I want to.
>>
>> If I put all the sprintf statements inside my loop then I get flooded with so many messages that makes it useless.
>>
>> Best Regards
>> Alex
>>
>> ______________________________________________
>> R-help at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>>
> 
> 
> 


- -- 
Rainer M. Krug, PhD (Conservation Ecology, SUN), MSc (Conservation
Biology, UCT), Dipl. Phys. (Germany)

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