[R] eval(parse(text vs. get when accessing a function

[Ramon Diaz-Uriarte]

On Friday 05 January 2007 19:35, Bert Gunter wrote:
> ??
>
> Or to add to what Peter Dalgaard said... (perhaps for the case of many more
> functions)
>
> Why eval(parse())? What's wrong with if then?
>
> g <- function(fpost,x){if(fpost==1)f.1 else f.2 }(x)
>
> or switch() if you have more than 2 possible arguments? I think your
> remarks reinforce the wisdom of Thomas's "axiom" .

Thanks, Bert, but as with Peter's solution, your solution forces me to build g 
ahead of time. And again, I am not sure I see why the attempt to avoid 
eval(parse(text.

Best,

R.


>
> Bert Gunter
> Genentech Nonclinical Statistics
> South San Francisco, CA 94404
>
>
> -----Original Message-----
> From: r-help-bounces at stat.math.ethz.ch
> [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Ramon Diaz-Uriarte
> Sent: Friday, January 05, 2007 10:02 AM
> To: r-help; rdiaz02 at gmail.com
> Subject: [R] eval(parse(text vs. get when accessing a function
>
> Dear All,
>
> I've read Thomas Lumley's fortune "If the answer is parse() you should
> usually
> rethink the question.". But I am not sure it that also applies (and why) to
> other situations (Lumley's comment
> http://tolstoy.newcastle.edu.au/R/help/05/02/12204.html
> was in reply to accessing a list).
>
> Suppose I have similarly called functions, except for a postfix. E.g.
>
> f.1 <- function(x) {x + 1}
> f.2 <- function(x) {x + 2}
>
> And sometimes I want to call f.1 and some other times f.2 inside another
> function. I can either do:
>
> g <- function(x, fpost) {
>     calledf <- eval(parse(text = paste("f.", fpost, sep = "")))
>     calledf(x)
>     ## do more stuff
> }
>
>
> Or:
>
> h <- function(x, fpost) {
>     calledf <- get(paste("f.", fpost, sep = ""))
>     calledf(x)
>     ## do more stuff
> }
>
>
> Two questions:
> 1) Why is the second better?
>
> 2) By changing g or h I could use "do.call" instead; why would that be
> better?
> Because I can handle differences in argument lists?
>
>
>
> Thanks,
>
>
> R.

-- 
Ramón Díaz-Uriarte
Centro Nacional de Investigaciones Oncológicas (CNIO)
(Spanish National Cancer Center)
Melchor Fernández Almagro, 3
28029 Madrid (Spain)
Fax: +-34-91-224-6972
Phone: +-34-91-224-6900

http://ligarto.org/rdiaz
PGP KeyID: 0xE89B3462
(http://ligarto.org/rdiaz/0xE89B3462.asc)



**NOTA DE CONFIDENCIALIDAD** Este correo electrónico, y en s...{{dropped}}