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

From: Bert Gunter <gunter.berton_at_gene.com>
Date: Fri 05 Jan 2007 - 18:35:42 GMT


??

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" .

Bert Gunter
Genentech Nonclinical Statistics
South San Francisco, CA 94404

-----Original Message-----
From: r-help-bounces@stat.math.ethz.ch
[mailto:r-help-bounces@stat.math.ethz.ch] On Behalf Of Ramon Diaz-Uriarte Sent: Friday, January 05, 2007 10:02 AM
To: r-help; rdiaz02@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}}

______________________________________________
R-help@stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.

______________________________________________
R-help@stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
Received on Sat Jan 06 12:21:38 2007

Archive maintained by Robert King, hosted by the discipline of statistics at the University of Newcastle, Australia.
Archive generated by hypermail 2.1.8, at Sat 06 Jan 2007 - 01:30:26 GMT.

Mailing list information is available at https://stat.ethz.ch/mailman/listinfo/r-help. Please read the posting guide before posting to the list.