R help - Oct 2009 - Re use objects from within a custom made function

Hi everyone,

i'm having a problem extracting objects out of functions i've created,
so i
can use them for further analysis. Here's a small example:

# ---------------------------
test <- function(i, j){
	x <- i:j
	y <- i*j
	z <- i/j
	return(x,y,z)
}
# ---------------------------

This returns the 3 objects as $x, $y and $z. I cannot, however, access these
objects individually by typing for example:

test$x

I know i can do this by adding an extra arrow head to the assignment arrow
(<<-), but I am sure that is not how it is done in some of the established
R
functions (like when calling lm$coef out of the lm function). Is there a
simple command i've omitted from the function that allows access to objects
inside it?

Thanks in advance,

Steve
-- 
View this message in context:
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Sent from the R help mailing list archive at Nabble.com.

test$x doesn't evaluate the function, you want something like test(1,2)$x,
e.g.:

test <- function(i, j){
	x <- i:j
	y <- i*j
	z <- i/j
	return(list(x=x,y=y,z=z))
}
> test(1,2)$x
[1] 1 2
> test(1,2)$y
[1] 2
> test(1,2)$z
[1] 0.5
> 
Or if you want to avoid evaluating your function multiple times:
> res <- test(1,2)
> res$x
[1] 1 2
> res$y
[1] 2
> res$z
[1] 0.5
> res
$x
[1] 1 2

$y
[1] 2

$z
[1] 0.5
> 

Stropharia wrote:
> Hi everyone,
> 
> i'm having a problem extracting objects out of functions i've
created, so i
> can use them for further analysis. Here's a small example:
> 
> # ---------------------------
> test <- function(i, j){
> 	x <- i:j
> 	y <- i*j
> 	z <- i/j
> 	return(x,y,z)
> }
> # ---------------------------
> 
> This returns the 3 objects as $x, $y and $z. I cannot, however, access
these
> objects individually by typing for example:
> 
> test$x
> 
> I know i can do this by adding an extra arrow head to the assignment arrow
> (<<-), but I am sure that is not how it is done in some of the
established R
> functions (like when calling lm$coef out of the lm function). Is there a
> simple command i've omitted from the function that allows access to
objects
> inside it?
> 
> Thanks in advance,
> 
> Steve

> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of Stropharia
> Sent: Monday, October 12, 2009 4:07 PM
> To: r-help at r-project.org
> Subject: [R] Re use objects from within a custom made function
> 
> 
> Hi everyone,
> 
> i'm having a problem extracting objects out of functions i've 
> created, so i
> can use them for further analysis. Here's a small example:
> 
> # ---------------------------
> test <- function(i, j){
> 	x <- i:j
> 	y <- i*j
> 	z <- i/j
> 	return(x,y,z)
> }
> # ---------------------------
> 
> This returns the 3 objects as $x, $y and $z. I cannot, 
> however, access these
> objects individually by typing for example:
> 
> test$x
> 
> I know i can do this by adding an extra arrow head to the 
> assignment arrow
> (<<-), but I am sure that is not how it is done in some of 
> the established R
> functions (like when calling lm$coef out of the lm function). 
> Is there a
> simple command i've omitted from the function that allows 
> access to objects
> inside it?
> 
> Thanks in advance,
> 
> Steve
> -- 
Steve,

I see a couple of problems (at least from my perspective).  If you ever got
your function to run, you would see a warning stating that returning
multiple objects is deprecated.  In your example of using the function, you
don't call it with any parameters, and the definition has no default values.
I also would be inclined to assign the results of the function call to a
variable/object and access the values from there. 

So I would approach your problem as follows:

test <- function(i, j){
	x <- i:j
	y <- i*j
	z <- i/j
	list(x=x, y=y, z=z)
}

my.result <- test(1,4)
> my.result$x
[1] 1 2 3 4
>
If you don't want to assign the output of test() to an object, then you will
need to do something like

test(1,4)$x

But this is inefficient because each time you access one of the components,
you need to rerun the function.

Hope this is helpful,

Dan

Daniel Nordlund
Bothell, WA USA

Thanks a lot Tony and Daniel for making that clear.

best,

Steve



Stropharia wrote:
> 
> Hi everyone,
> 
> i'm having a problem extracting objects out of functions i've
created, so
> i can use them for further analysis. Here's a small example:
> 
> # ---------------------------
> test <- function(i, j){
> 	x <- i:j
> 	y <- i*j
> 	z <- i/j
> 	return(x,y,z)
> }
> # ---------------------------
> 
> This returns the 3 objects as $x, $y and $z. I cannot, however, access
> these objects individually by typing for example:
> 
> test$x
> 
> I know i can do this by adding an extra arrow head to the assignment arrow
> (<<-), but I am sure that is not how it is done in some of the
established
> R functions (like when calling lm$coef out of the lm function). Is there a
> simple command i've omitted from the function that allows access to
> objects inside it?
> 
> Thanks in advance,
> 
> Steve
> 
-- 
View this message in context:
http://www.nabble.com/Reuse-objects-from-within-a-custom-made-function-tp25864695p25866081.html
Sent from the R help mailing list archive at Nabble.com.

On Oct 12, 2009, at 7:06 PM, Stropharia wrote:
>
> Hi everyone,
>
> i'm having a problem extracting objects out of functions i've  
> created, so i
> can use them for further analysis. Here's a small example:
>
> # ---------------------------
> test <- function(i, j){
> 	x <- i:j
> 	y <- i*j
> 	z <- i/j
> 	return(x,y,z)
> }
> # ---------------------------
>
> This returns the 3 objects as $x, $y and $z. I cannot, however,  
> access these
> objects individually by typing for example:
>
> test$x

Generally one assigns the resutlts of a function to an object name:

 > ll <- test(1,2)
Warning message:
In return(x, y, z) : multi-argument returns are deprecated
 > ll
$x
[1] 1 2

$y
[1] 2

$z
[1] 0.5

 > str(ll)
List of 3
  $ x: int [1:2] 1 2
  $ y: num 2
  $ z: num 0.5


So you would not get the warnings if you instead ended the function  
with:

  return(list(x,y,z) )
>
> I know i can do this by adding an extra arrow head to the assignment  
> arrow
> (<<-), but I am sure that is not how it is done in some of the  
> established R
> functions (like when calling lm$coef out of the lm function). Is  
> there a
> simple command i've omitted from the function that allows access to  
> objects
> inside it?
>
> Thanks in advance,
>
> Steve
> -- 
--

David Winsemius, MD
Heritage Laboratories
West Hartford, CT