'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-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On
Behalf Of Saptarshi Guha
Sent: Friday, 17 July 2009 5:16 PM
To: R-help@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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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
