[R] Remembering a value in multiple calls of a function

[Saptarshi Guha]

Thanks to all for the helpful explanation.
Regards
Saptarshi

On Fri, Jul 17, 2009 at 12:42 AM, <Bill.Venables at csiro.au> wrote:
> 'startgiven' is in the environment of your function 'incr' (which is what your function 'a' becomes).  It might be more transparent to define your function with an enclosing local environment explicitly, for example:
>
>> b <- local({
> +   startgiven <- 0
> +   function(n) {
> +     if(!missing(n)) {
> +       startgiven <<- n
> +     } else {
> +       startgiven <<- startgiven + 1
> +     }
> +     startgiven
> +   }
> + })
>> b(5)
> [1] 5
>> b()
> [1] 6
>> b()
> [1] 7
>>
>
> You should look carefully at the help information for the superassignment operator
>
> help("<<-")
>
> to see precisely where assignments made by this operator are located.
>
>
> Bill Venables
> http://www.cmis.csiro.au/bill.venables/
>
>
> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf Of Saptarshi Guha
> Sent: Friday, 17 July 2009 5:16 PM
> To: R-help at r-project.org
> Subject: [R] Remembering a value in multiple calls of a function
>
> Hello,
> I tried this pseudo-generator style experiment (see below). The "<<-"
> operator assigns to in the calling environment which would be the
> environment of  "getN".
> Yet when the function incr is returned, isn't this environment lost?
> Also the print displays GlobalEnv, yet the globalenv does not have any
> mention of startgiven.
> This code was inspired from and old issue of RJournal , but I'm not
> sure how this works.
>
> I'm not sure how this works and an explanation would be helpful.
>
> Thank you
> Saptarshi
>
> getN <- function(start){
>  startgiven <- start;
>  incr <- function(n=NA){
>    print(parent.frame())
>    if(!is.na(n)) startgiven<<-n
>    startgiven<<-startgiven+1
>    return(startgiven)
>  }
> }
> a=getN(10)
> a() #11
> a()#12
>
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