R help - Aug 2012 - pass by reference

Hi all,

I want to do the following:

data<-data.frame(col1=c(1,2,3,4,5))

getcol2<-function(data){
    data$col2[data$col1<=2]="L"
}

getcol2(data)

Unfortunately in the above col2 does not appear in the final data. So how
would you pass this by reference such that you would get it back?

Thanks,
Sachin

	[[alternative HTML version deleted]]

You have to return the value of 'data' from the function.  Functions
do not have "side effects".
> data<-data.frame(col1=c(1,2,3,4,5))
>
> getcol2<-function(data){
+     data$col2[data$col1<=2]="L"
+     data  # return value
+ }
>
> getcol2(data)
  col1 col2
1    1    L
2    2    L
3    3 <NA>
4    4 <NA>
5    5 <NA>
>

On Mon, Aug 13, 2012 at 9:08 PM, Sachinthaka Abeywardana
<sachin.abeywardana at gmail.com> wrote:
> Hi all,
>
> I want to do the following:
>
> data<-data.frame(col1=c(1,2,3,4,5))
>
> getcol2<-function(data){
>     data$col2[data$col1<=2]="L"
> }
>
> getcol2(data)
>
> Unfortunately in the above col2 does not appear in the final data. So how
> would you pass this by reference such that you would get it back?
>
> Thanks,
> Sachin
>
>         [[alternative HTML version deleted]]
>
> ______________________________________________
> 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.


-- 
Jim Holtman
Data Munger Guru

What is the problem that you are trying to solve?
Tell me what you want to do, not how you want to do it.

HI,
Try this:
getcol2<-function(data){
??? data$col2[data$col1<=2]="L"
?data
?}
data<-getcol2(data)
?data
#? col1 col2
#1??? 1??? L
#2??? 2??? L
#3??? 3 <NA>
#4??? 4 <NA>
#5??? 5 <NA>
A.K.



----- Original Message -----
From: Sachinthaka Abeywardana <sachin.abeywardana at gmail.com>
To: r-help at r-project.org
Cc: 
Sent: Monday, August 13, 2012 9:08 PM
Subject: [R] pass by reference

Hi all,

I want to do the following:

data<-data.frame(col1=c(1,2,3,4,5))

getcol2<-function(data){
? ? data$col2[data$col1<=2]="L"
}

getcol2(data)

Unfortunately in the above col2 does not appear in the final data. So how
would you pass this by reference such that you would get it back?

Thanks,
Sachin

??? [[alternative HTML version deleted]]

______________________________________________
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.

Hi Sachinthaka,
You can do it in the following way:

getcol2<-function(data){
  data$col2[data$col1<=2]="L"
  data<<-data
 }

<<- writes the result to  the underlying environment. This is however
generally seen as very bad programming (side effects).
Greet'
Frans-----Oorspronkelijk bericht-----
Van: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
Namens Sachinthaka Abeywardana
Verzonden: dinsdag 14 augustus 2012 3:08
Aan: r-help at r-project.org
Onderwerp: [R] pass by reference

Hi all,

I want to do the following:

data<-data.frame(col1=c(1,2,3,4,5))

getcol2<-function(data){
    data$col2[data$col1<=2]="L"
}

getcol2(data)

Unfortunately in the above col2 does not appear in the final data. So how
would you pass this by reference such that you would get it back?

Thanks,
Sachin

	[[alternative HTML version deleted]]

______________________________________________
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.

You can use macros for this effect. Or environments:

daf <- data.frame(a=1:10, b=rnorm(10))
env <- as.environment(daf)

fun <- function(x) x$c <- x$a+x$b
fun(daf)
fun(env)

daf$c
env$c

You can see that the same function (fun) changes one object but leaves
another one unchanged. But before using it for something important,
think of the side effects and efficiency. Passing by value does not
create as many unnecessary copies as one might think.

On Tue, Aug 14, 2012 at 4:08 AM, Sachinthaka Abeywardana
<sachin.abeywardana at gmail.com> wrote:
> Hi all,
>
> I want to do the following:
>
> data<-data.frame(col1=c(1,2,3,4,5))
>
> getcol2<-function(data){
>     data$col2[data$col1<=2]="L"
> }
>
> getcol2(data)
>
> Unfortunately in the above col2 does not appear in the final data. So how
> would you pass this by reference such that you would get it back?
>
> Thanks,
> Sachin
>
>         [[alternative HTML version deleted]]
>
> ______________________________________________
> 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.