[R] assigning from multiple return values

[Liaw, Andy]

My $0.02:

If Jack feels that the fact that functions usually return a single list, and
one needs to access the components of the list separately, is somehow
hideous, then I'd rather suggest that R is perhaps the wrong language for
him.

To me the suggested `workarounds' are by far much more hideous...  They turn
perfectly tranparent code into...  gee, I don't even know how to begin
describing them...

Andy

> From: Gabor Grothendieck
> 
> 
> Here are two approaches assuming foo is "zz" and bar is 3.
> 
> FIRST
> 
> You could pass the return variables in the argument list and then
> assign them in the caller's frame like this:
> 
> fn <- function(x,y) {
> 	assign(as.character(substitute(x)), "zz", sys.frame(-1))
> 	assign(as.character(substitute(y)), 3, sys.frame(-1))
> }
> fn(a,b)  # sets a to "zz" and b to 3
> 
> SECOND
> 
> You can make this a bit prettier, though not perfect, like this:
> 
> 
> "list2<-" <- function(x,y,value) {
> 	assign(as.character(substitute(y)), value[[2]], sys.frame(-1))
> 	value[[1]]
> }
> fn <- function()list("zz",3)
> a <- 1 # first arg must exist prior to invoking list2. Its 
> value not important.
> list2(a,b) <- fn()
> 
> 
> The two problems with list2 are:
> 
> 1. the first argument must exist prior to invoking list2 although its
> actual value is immaterial since it just gets overwritten anyways.
> 
> 2. It only works for 2 args although you could write a list3, 
> list4, etc.
> 
> Maybe someone could comment on these deficiencies.
> 
> 
> Jack Tanner <ihok <at> hotmail.com> writes:
> 
> : 
> : I know that if I have a function that returns multiple 
> values, I should
> : do return(list(foo, bar)). But what do I do on the recieving end?
> : 
> : fn <- function(x) {
> :    return(list(foo, bar))
> : }
> : 
> : I know that at this point I could say
> : 
> : values.list <- fn(x)
> : 
> : and then access
> : 
> : values.list[1]
> : values.list[2]
> : 
> : But that's hideous. I'd rather be able to say something like
> : 
> : list(local_foo, local_bar) <- fn(x)
> : 
> : and have the right thing happen. I realize that it's my 
> responsibility
> : to not screw up and say instead
> : 
> : list(local_bar, local_foo)
> : 
> : Any suggestions?
> : 
> : -JT
> :
> 
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