R help - May 2004 - accessing function arguments as text, macro style

Hi.  In a case like this, I can get strip headings that have the name
"c" and the value for c.

  d <- data.frame(a=1:5,b=6:10,c=11:15)
  > xyplot(a ~ b | paste("c", c), data=d)
  > 

For more complicated examples, instead of using paste repeatedly I
would like to use a function.  It seems like what I really want is a
macro, though.  I'm not quite familiar enough with R's treatment of
function parameters to know how to do something like this (ficticious
example):

  f <- function(x) { paste(identifier(x), value(x)) }
  > rambo <- "brave"
  > f(rambo)
  "rambo brave"

I've checked ?function, ?args, ?eval, and some others, but I think
I'm barking up the wrong tree.  Any pointers would be most
appreciated. 
  
-- 
--Ed L Cashin            |   PGP public key:
  ecashin at uga.edu        |   http://noserose.net/e/pgp/

Ed L Cashin <ecashin <at> uga.edu> writes:
> function parameters to know how to do something like this (ficticious
> example):
> 
>   f <- function(x) { paste(identifier(x), value(x)) }
>   > rambo <- "brave"
>   > f(rambo)
>   "rambo brave"

R> f <- function(x) paste(as.character(substitute(x)),x)
R> z <- 3
R> f(z)
[1] "z 3"

Gabor Grothendieck <ggrothendieck at myway.com> writes:

...
> R> f <- function(x) paste(as.character(substitute(x)),x)
> R> z <- 3
> R> f(z)
> [1] "z 3"
Fantastic.  Works like a charm.  

-- 
--Ed L Cashin            |   PGP public key:
  ecashin at uga.edu        |   http://noserose.net/e/pgp/

This solution may not quite work as you intend. I believe that the preferred
solution is:
 f <- function(x) paste(deparse(substitute(x)),x)

This would give the same result with the z<-3 example below, but try it for
both
versions with the call:
f(sin(3))

The subtlety is that substitute returns the parse TREE of its
(expression)argument, which you probably want deparsed rather than cast by
as.character().

Cheers,
Bert

Ed L Cashin wrote:
> Gabor Grothendieck <ggrothendieck at myway.com> writes:
>
> ...
> > R> f <- function(x) paste(as.character(substitute(x)),x)
> > R> z <- 3
> > R> f(z)
> > [1] "z 3"
>
> Fantastic.  Works like a charm.
>
> --
> --Ed L Cashin            |   PGP public key:
>   ecashin at uga.edu        |   http://noserose.net/e/pgp/
>
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--

Bert Gunter

Non-Clinical Biostatistics
Genentech
MS: 240B
Phone: 650-467-7374


"The business of the statistician is to catalyze the scientific learning
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