[R] Return variable assignments from a function

[Scott Hyde]

As a followup to my question yesterday, what if I were to return the
argument as a list, and then "unwrap" the list with the function I've
written called "objects".  Is there any problems with doing it?  It
works to use it inside other functions.  For example:

=================================

> objects <- function(alist) {
  for (vars in names(alist))
    assign(vars,alist[[vars]],pos=sys.frame(-1))
}

> simple <- function(m,n) {
  A=matrix(c(3,3,2,3),2,2)
  B=m
  c=1:n
  list(A=A,B=B,c=c)
}
> rm(A,B,c)  #just in case they exist
> stuff=simple(2,3)
> objects(stuff)
> A
     [,1] [,2]
[1,]    3    2
[2,]    3    3
> B
[1] 2
> c
[1] 1 2 3
>

=================================

-Scott


*****************************************************************
Scott K. Hyde
Assistant Professor of Statistics and Mathematics
College of Math and Sciences
Brigham Young University -- Hawaii
Laie, HI  96762



On Tue, Jun 2, 2009 at 5:30 PM, Scott Hyde <hydes at byuh.edu> wrote:
>
> I'd like to perform return variable assignments like matlab.  For example, the following function would return A, B, and c to the script that called it.
>
> =================================
> function  [A,B,c] = simple(m,n)
> A=[ 3 2; 3 3]
> B=m
> c=1:n
> =================================
>
> I'd like to do similar assignments in R, but I seem to be able to only return one variable.  I tried to use a list to return all the arguments, but then each has to be referred to using the list.  For example:
>
> =================================
> simple <- function(m,n) {
>   A=matrix(c(3,3,2,3),2,2)
>   B=m
>   c=1:n
>   list(A=A,B=B,c=c)
> }
>
> > stuff=simple(2,3)
> > stuff
> $A
>      [,1] [,2]
> [1,]    3    2
> [2,]    3    3
>
> $B
> [1] 2
>
> $c
> [1] 1 2 3
> =================================
>
> Then I could assign each variable like this (which is what I'd like to avoid):
>
> =================================
> A=stuff$A
> B=stuff$B
> c=stuff$c
> rm(stuff)   #stuff isn't needed anymore.
> =================================
>
>
> I've even toyed with the superassignment operator, which also works, but I think it doesn't work for functions of functions.  The following example works.
>
> =================================
> simple2 <- function(m,n) {
>   A <<- matrix(c(3,3,2,3),2,2)
>   B <<- m
>   c <<- 1:n
> }
>
> > stuff2=simple2(2,3)
> > stuff2
> [1] 1 2 3
> > A
>      [,1] [,2]
> [1,]    3    2
> [2,]    3    3
> > B
> [1] 2
> > c
> [1] 1 2 3
> =================================
>
> In the example below, I call the function ten inside the function nine.  I'm expecting that the variable b should change only in the function nine (and not in the global environment).  In other words, I think the line "(nine) b= 9" should be "(nine) b= 10".
>
> Can someone help me know how to do this correctly?
>
> -Scott
>
> =================================
> nine = function(a) {
>   b <- 9
>   ten(a)
>   print(paste("(nine) b=",b))
> }
>
> ten = function(d) {
>   b <<- 10
>   print(paste("(ten) b=",b))
>   print(paste("(ten) d=",d))
>   d
> }
>
> > nine(5)
> [1] "(ten) b= 10"
> [1] "(ten) d= 5"
> [1] "(nine) b= 9"
> > b
> [1] 10
> =================================
>