[R] defining a template for functions via do.call and substitute.

[Thomas Lumley]

On Wed, 29 Sep 2004, Berton Gunter wrote:

> John:
>
> Andy and Dimitris have already fully answered your query. However, as you
> seem to mainly be interested in simple string substitution, I wanted to
> point out that there is a perhaps more transparent approach using gsub()
> that does just this.
>
> Here's a slightly more complicated function form to illustrate the idea:
>
>> f<-function(a,b){z<-a+b; b+z*sin(b)}
>
>> ## Get the body of the function and convert it to a character vector:
>>  bf<-deparse(body(f))
>
>> orig<-c('a','b')  ## original symbols
>> changed<-c('x','y') ## the character strings you wish to substitute for
> them

The problem with this is that it will substitute xx for aa, and xy for ab, 
and so on.  You need at least to tokenize the code, even if you don't 
necessarily need to parse it.

 	-thomas


>> ## perform the string substitution
>>  for(i in seq(along=changed))bf<-gsub(orig[i],changed[i],bf)
>
>> ## re-parse the body and change the formals
>>  body(f)<-parse(text=bf)
>>  names(formals(f))<-changed
>
>> f
> function (x, y)
> {
>    z <- x + y
>    y + z * sin(y)
> }
>
> substitute's real power lies in its ability to substitute whole expressions
> bound to a symbol in an environment, and this might be overkill here.
>
> Cheers,
>
> -- Bert Gunter
> Genentech Non-Clinical Statistics
> South San Francisco, CA
>
> "The business of the statistician is to catalyze the scientific learning
> process."  - George E. P. Box
>
>
>
>> -----Original Message-----
>> From: r-help-bounces at stat.math.ethz.ch
>> [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of
>> john.gavin at ubs.com
>> Sent: Wednesday, September 29, 2004 4:17 AM
>> To: r-help at stat.math.ethz.ch
>> Subject: [R] defining a template for functions via do.call
>> and substitute.
>>
>> Hi,
>>
>> Given a function
>>
>>   fun <- function(a, b) a + b
>>
>> how do I generate the function 'function(x, y) x + y'?
>>
>> Working from the help files and Bill Venables' R-news article
>> (June 2002),
>> I have tried various permutations with substitute without success.
>> e.g.
>>   do.call("substitute", list(fun, list(a = as.name("x"), b =
>> as.name("y"))))
>>
>> Regards,
>>
>> John.
>>
>> John Gavin <john.gavin at ubs.com>,
>> Quantitative Risk Models and Statistics,
>> UBS Investment Bank, 6th floor,
>> 100 Liverpool St., London EC2M 2RH, UK.
>> Phone +44 (0) 207 567 4289
>> Fax   +44 (0) 207 568 5352
>>
>> Visit our website at http://www.ubs.com
>>
>> This message contains confidential information and is
>> intend...{{dropped}}
>>
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>
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Thomas Lumley			Assoc. Professor, Biostatistics
tlumley at u.washington.edu	University of Washington, Seattle