Return a list

Dear R Users,

another problem for me is the output of a function.

I have several output variables which I give back with the list  
command.

test <- function	{return(list(a,b,c,d,e,f,g,...))}

After the usage of the function I want to assign the variables to  
the output variables.

result <- test()

a <- result$a
b <- result$b
c <- result$c
d <- result$d
...

is there a more elegant way to assign these variables, without  
writing them all down?

thank you very much for your help!

Stefan Fritsch

Dear R Users,

another problem for me is the output of a function.

I have several output variables which I give back with the list command.

test <- function        {return(list(a,b,c,d,e,f,g,...))}

After the usage of the function I want to assign the variables to the output variables.

result <- test()

a <- result$a
b <- result$b
c <- result$c
d <- result$d
...

is there a more elegant way to assign these variables, without writing them all down?

thank you very much for your help!

Stefan Fritsch

I have several output variables which I give back with the list command.

test <- function	{return(list(a,b,c,d,e,f,g,...))}

After the usage of the function I want to assign the variables to the output variables.

result <- test()

a <- result$a
b <- result$b
c <- result$c
d <- result$d
...

is there a more elegant way to assign these variables, without writing them all down?

thank you very much for your help!

"Stefan Fritsch" <fritsch at bips.uni-bremen.de> wrote:

  

I have several output variables which I give back with the list command.

test <- function	{return(list(a,b,c,d,e,f,g,...))}

After the usage of the function I want to assign the variables to the output variables.

result <- test()

a <- result$a
b <- result$b
c <- result$c
d <- result$d
...

is there a more elegant way to assign these variables, without writing them all down?

    

"Stefan Fritsch" <fritsch at bips.uni-bremen.de> wrote:

  

I have several output variables which I give back with the list command.

test <- function	{return(list(a,b,c,d,e,f,g,...))}

After the usage of the function I want to assign the variables to the

result <- test()

a <- result$a
b <- result$b
c <- result$c
d <- result$d
...

is there a more elegant way to assign these variables, without writing

But why do this? Just leave the (preferably named) variables as list
components and work with them there.

1. ?comment tells you how to add a comment attribute to the list for self
documentation (what were the components? how are they related? etc.)

2. ?with  shows you how to access the components of the list individually in
the "usual" way.

3. ?lapply and friends shows you how to "loop" over list components .

etc.

Cheers,
Bert

Bert Gunter 
Genentech  

  

I have several output variables which I give back with the list command.

test <- function	{return(list(a,b,c,d,e,f,g,...))}

After the usage of the function I want to assign the variables to the
      

output variables.
  

result <- test()

a <- result$a
b <- result$b
c <- result$c
d <- result$d
...

is there a more elegant way to assign these variables, without writing
      

them all down?
  

arguably ugly and risky, but simple:

for (name in names(result)) assign(name, result[[name]])

(note, for this to work you actually need to name the components of the
returned list: return(list(a=a,b=b,...)))

vQ

The answers that were previously given allow you to easily extract results
from your returned list, but if I understand well, this list is created only
because you cannot return several arguments whereas you need to keep the
values of a, b, c, etc. Am I right?
Another solution would be to directly "send" the values you want to keep
into the environment where they are needed. The following example supposes
you need to keep "a" only in the upper environment from which your function
was launched, and "b" in another one (e.g. .GlobalEnv).
Hope this may help.
Nael

  

# Here is a function such as yours:
test <- function(){
    

+ a <- 1
+ b <- 2
+ return(list(a=a, b=b, c=c))
+ }
  

result <- test()
(a <- result$a)
    

[1] 1
  

(b <- result$b)
    

[1] 2
  

rm(a, b)

# Now our variables will be automatically assigned into the chosen
    

environment
  

test2 <- function(){
    

+ a <- 1
+ b <- 2
+ assign("a", a, envir=parent.frame(n=1))
+ assign("b", b, envir=.GlobalEnv)
+ return(NULL)
+ }
  

# Suppose test2 is launched by another function
test2.launcher <- function() {
    

+ test2()
+ print(paste("a exists inside test2.launcher:", exists("a")))
+ print(paste("b exists inside test2.launcher:", exists("b")))
+ return (NULL)
+ }

  

test2.launcher()
    

[1] "a exists inside test2.launcher: TRUE"
[1] "b exists inside test2.launcher: TRUE"
NULL
  

exists("a")# a still exists in the upper environment
    

[1] FALSE
  

exists("b")# b does not
    

[1] TRUE

it depends on what the original author wanted.

with constructs a new environment, and all assignments, if any, made in
the expression evaluated within with are invisible to the outside
(unless one plays with environments, again):

x = 1:10
a = 3
with(test(), { x[1:3] = c(a,b,c); x = x+d; a = a + 1 })
x # still 1:10, whatever test returns
a # still 3. whatever test returns

if the author wanted the values included in the list to be visible and
accessible by simple names, and used in assignments in a larger part of
code, using with might be inconvenient.