R help - Nov 2012 - transform input argument (matrix) of function

Dear list!
 
I would like to write a function to transform matrix, which is input argument of
a written function. It is easy with new matrix (see below), but my idea is to
transform input argument (matrix) of function without any additional matrixes.
Here is an example:

fun1 <- function(xy) {
xy <- cbind(xy[,1], xy[,2], xy[,1] + xy[,2])
return(xy)
}
 
df1 <- matrix(c(1,2,3,1,2,3), ncol = 2)
fun1(df1)
 
fun2 <- function(xy) {
xy <- cbind(xy[,1], xy[,2], xy[,1] + xy[,2])
return(invisible(xy))
}
 
fun2(df1)
df1
> should be
     [,1] [,2] [,3]
[1,]    1    1    2
[2,]    2    2    4
[3,]    3    3    6
 
Thanks to all for help,
OV
	[[alternative HTML version deleted]]

I'm afraid I don't really understand what you're searching for, but
note that your functions can be written without assignment/return:

fun3 <- function(x) invisible(cbind(xy[,1], xy[,2], xy[,1] + xy[,2]))

Cheers,
Michael

On Sat, Nov 17, 2012 at 3:41 PM, Omphalodes Verna
<omphalodes.verna at yahoo.com> wrote:
> Dear list!
>
> I would like to write a function to transform matrix, which is input
argument of a written function. It is easy with new matrix (see below), but my
idea is to transform input argument (matrix) of function without any additional
matrixes. Here is an example:
>
> fun1 <- function(xy) {
> xy <- cbind(xy[,1], xy[,2], xy[,1] + xy[,2])
> return(xy)
> }
>
> df1 <- matrix(c(1,2,3,1,2,3), ncol = 2)
> fun1(df1)
>
> fun2 <- function(xy) {
> xy <- cbind(xy[,1], xy[,2], xy[,1] + xy[,2])
> return(invisible(xy))
> }
>
> fun2(df1)
> df1
>> should be
>      [,1] [,2] [,3]
> [1,]    1    1    2
> [2,]    2    2    4
> [3,]    3    3    6
>
> Thanks to all for help,
> OV
>         [[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.
>

Hello,

Your function fun2 (in fact both of them) changes a _copy_ of df1, not 
df1 itself. To have a copy of the output of fun2 you need to assign the 
value of fun2 outside it.

df2 <- fun2(df1)

Now df2 has what you want. (If I understand it well.)

Hope this helps,

Rui Barradas
Em 17-11-2012 15:41, Omphalodes Verna escreveu:
> Dear list!
>   
> I would like to write a function to transform matrix, which is input
argument of a written function. It is easy with new matrix (see below), but my
idea is to transform input argument (matrix) of function without any additional
matrixes. Here is an example:
>
> fun1 <- function(xy) {
> xy <- cbind(xy[,1], xy[,2], xy[,1] + xy[,2])
> return(xy)
> }
>   
> df1 <- matrix(c(1,2,3,1,2,3), ncol = 2)
> fun1(df1)
>   
> fun2 <- function(xy) {
> xy <- cbind(xy[,1], xy[,2], xy[,1] + xy[,2])
> return(invisible(xy))
> }
>   
> fun2(df1)
> df1
>> should be
>       [,1] [,2] [,3]
> [1,]    1    1    2
> [2,]    2    2    4
> [3,]    3    3    6
>   
> Thanks to all for help,
> OV
> 	[[alternative HTML version deleted]]
>
>
>
> ______________________________________________
> R-help@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.

	[[alternative HTML version deleted]]

On Nov 17, 2012, at 7:41 AM, Omphalodes Verna wrote:
> Dear list!
>
> I would like to write a function to transform matrix, which is input  
> argument of a written function. It is easy with new matrix (see  
> below), but my idea is to transform input argument (matrix) of  
> function without any additional matrixes. Here is an example:
>
> fun1 <- function(xy) {
> xy <- cbind(xy[,1], xy[,2], xy[,1] + xy[,2])
> return(xy)
> }
>
> df1 <- matrix(c(1,2,3,1,2,3), ncol = 2)
> fun1(df1)
>
> fun2 <- function(xy) {
> xy <- cbind(xy[,1], xy[,2], xy[,1] + xy[,2])
> return(invisible(xy))
> }
>
> fun2(df1)
> df1
>> should be
No, it should not be a three column matrix. When you call a function  
with an appropriate argument and fail fail to assign it to anything,  
the result evaporates.

?'<-'
?assign

Functions generally do not modify objects "in place". If you wanted to
have df1 be the result of fun2(df1) you would have needed to do this:

df1 <- fun2(df1)

  There are ways to get around that limitation (described in each of  
those help pages), but I think it is better for one to learn ordinary  
functional programming conventions first.
>      [,1] [,2] [,3]
> [1,]    1    1    2
> [2,]    2    2    4
> [3,]    3    3    6
>
> Thanks to all for help,
> OV
> 	[[alternative HTML version deleted]]
This persistent practice after multiple postings to Rhelp  marks you  
as someone either having difficulty in reading the Posting Guide.
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
-- 
David Winsemius, MD
Alameda, CA, USA