[R] assigning from multiple return values

[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
: