R help - Sep 2009 - Basic function output/scope question

Hello Group,

I'm trying to learn R and am having a problem getting output from a
function I'm trying to write.  The problem is clearly one of scope,
but I can't find the documentation that tells me how to get around the
issue.

Here is an example of my problem.

testfunc<-function(x)
{ y<-10
print(y)
print(x)
}

testfunc(4)

The variables x and y are accessible during execution of the function
"testfunc" but not afterwards.  I've read through the Introduction
to
R, and the R language definition on functions, but do not see how to
define the output of the function, or change the scope of a function
variable using the R equivalent of a %global statement as would be
done in SAS.  Can someone tell me either where I can look for more
information or how to make x and y accessible to operations after the
function is run?

Thanks in advance for any suggestions.



-- 
Best regards,

David Young
Marketing and Statistical Consultant
Madrid, Spain
+34 913 540 381
http://www.linkedin.com/in/europedavidyoung

                          mailto:dyoung at telefonica.net

Don't know SAS, but you can use y<<-10 to make the answer available in
the global environement.  See ?'<<-'
To define the output see ?return

Schalk Heunis


On Mon, Sep 21, 2009 at 5:29 PM, David Young <dyoung at telefonica.net>
wrote:
> Hello Group,
>
> I'm trying to learn R and am having a problem getting output from a
> function I'm trying to write. ?The problem is clearly one of scope,
> but I can't find the documentation that tells me how to get around the
> issue.
>
> Here is an example of my problem.
>
> testfunc<-function(x)
> { y<-10
> print(y)
> print(x)
> }
>
> testfunc(4)
>
> The variables x and y are accessible during execution of the function
> "testfunc" but not afterwards. ?I've read through the
Introduction to
> R, and the R language definition on functions, but do not see how to
> define the output of the function, or change the scope of a function
> variable using the R equivalent of a %global statement as would be
> done in SAS. ?Can someone tell me either where I can look for more
> information or how to make x and y accessible to operations after the
> function is run?
>
> Thanks in advance for any suggestions.
>
>
>
> --
> Best regards,
>
> David Young
> Marketing and Statistical Consultant
> Madrid, Spain
> +34 913 540 381
> http://www.linkedin.com/in/europedavidyoung
>
> ? ? ? ? ? ? ? ? ? ? ? ? ?mailto:dyoung at telefonica.net
>
> ______________________________________________
> 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.
>

Hello, 
> 
> testfunc<-function(x)
> { y<-10
> print(y)
> print(x)
> }
> 
> testfunc(4)
> 
> The variables x and y are accessible during execution of the function
> "testfunc" but not afterwards.  
In R, expressions return values.  When you define a function, ?function says
that, "If the end of a function is reached without calling
'return', the value of the last evaluated expression is returned."

So you are correct, 'x' and 'y' are local variables, and by all
accounts they should be.  If you want their values accessible, simply return
them.

## return just y
testfunc2 <- function(x) {
   y <- 10
   y
}

## return both x and y 
testfunc2 <- function(x) {
   y <- 10
   list(x, y)
}

There are ways to make x and y global from within a function, but in general
that is not the R way to do things!

Hope that helps, 
Erik Iverson

On Sep 21, 2009, at 11:29 AM, David Young wrote:
> Hello Group,
>
> I'm trying to learn R and am having a problem getting output from a
> function I'm trying to write.  The problem is clearly one of scope,
> but I can't find the documentation that tells me how to get around the
> issue.
>
> Here is an example of my problem.
>
> testfunc<-function(x)
> { y<-10
> print(y)
> print(x)
> }
>
> testfunc(4)
The print function calls done inside testfunc have side effects of  
printing to the console. See this additional code that demonstrates  
that the returned value is actually "x" which is the last evaluated  
object in the function. You should also look at the "return" function.

 > z<-testfunc(4)
[1] 10   # side-effect but NOT the returned value
[1] 4
 > z
[1] 4   # the returned value

?return

-- 
David.
>
> The variables x and y are accessible during execution of the function
> "testfunc" but not afterwards.  I've read through the
Introduction to
> R, and the R language definition on functions, but do not see how to
> define the output of the function, or change the scope of a function
> variable using the R equivalent of a %global statement as would be
> done in SAS.  Can someone tell me either where I can look for more
> information or how to make x and y accessible to operations after the
> function is run?
>
> Thanks in advance for any suggestions.
>
>
>
> -- 
> Best regards,
>
> David Young
> Marketing and Statistical Consultant
> Madrid, Spain
> +34 913 540 381
> http://www.linkedin.com/in/europedavidyoung
>
>                          mailto:dyoung at telefonica.net
>
> ______________________________________________
> 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.
David Winsemius, MD
Heritage Laboratories
West Hartford, CT