R help - Jun 2009 - changing default arguments of a function and return the modified function as a result

Dear R-users, 

I am trying to develop a function that takes another function as an argument, 
changes its default values and returns a list of things, among which the 
initial function with its default arguments changed. An example of what i 
will like to obtain below:

## initial function

myfun <- function(x, a=19, b=21){ return(a * x + b) }

## this is the function i will like to create 
## (does not work as it is written here)

mysecond.fun <- function(a, b, c = myfun(a=2, b=15)){
return(list(a=a, b=b c=c))
}

So I would be able to call:

mysecond.fun$c(x=12)

And this will be equivalent of calling:

myfun(x=12, a=2, b=15 ) ## i.e. i have changed the default values of myfun and
			## stored it in a new function mysecond.fun$c

Any help will be greatly appreciated!

Miguel Bernal.


----
Current address:							
Ocean Modeling group, 			
Institute of Marine and Coastal Sciences
University of Rutgers			
71 Dudley Road, New Brusnkwick, 
New Jersey 08901, USA			
email: mbernal at marine.rutgers.edu
phone: +1 732 932 3692			
Fax: +1 732 932 8578		
---------------------------------------------
Permanent address:
Instituto Espa?ol de Oceanograf?a	
Centro Oceanogr?fico de C?diz
Puerto Pesquero, Muelle de Levante, s/n
Apdo. 2609, 11006 C?diz, Spain
email: miguel.bernal at cd.ieo.es
phone: +34 956 294189
Fax: +34 956 294232

On Jun 26, 2009, at 12:52 PM, Miguel Bernal wrote:
> Dear R-users,
>
> I am trying to develop a function that takes another function as an  
> argument,
> changes its default values and returns a list of things, among which  
> the
> initial function with its default arguments changed. An example of  
> what i
> will like to obtain below:
>
> ## initial function
>
> myfun <- function(x, a=19, b=21){ return(a * x + b) }
>
> ## this is the function i will like to create
> ## (does not work as it is written here)
>
> mysecond.fun <- function(a, b, c = myfun(a=2, b=15)){
                                  ^^^^^^^^^^^^^^^^^^
Two things: a) I doubt that is possible in that manner and b) you  
couldn't possibly get myfun to work, because you are not passing it  
the correct number of arguments.

> return(list(a=a, b=b c=c))
                      ^
Third concern, missing comma.
> }
>
> So I would be able to call:
>
> mysecond.fun$c(x=12)
Not in this language. Maybe in some other. Maybe you are in the wrong  
help list? You should instead provide a specification of the inputs  
and outputs you expect rather than a hashed up view of how you think R  
should accept functional arguments.

Perhaps something like this:

myfun <- function(x, a=19, b=21){ return(a * x + b) }
mysecond.fun <- function(x, a, b){ c <- myfun(x, a=2, b=15)
   list(a=a, b=b, c=c)  }

 > mysecond.fun(x=12, 2 , 3)
$a
[1] 2

$b
[1] 3

$c
[1] 39

 > # c= 2 * 12 + 15
>
> And this will be equivalent of calling:
>
> myfun(x=12, a=2, b=15 ) ## i.e. i have changed the default values of  
> myfun and
> 			## stored it in a new function mysecond.fun$c
>
> Any help will be greatly appreciated!
>
> Miguel Bernal.
David Winsemius, MD
Heritage Laboratories
West Hartford, CT

Is this what you want?

myfun <- function(x, a=19, b=21){ return(a * x + b) }

mysecond.fun <- function(a, b, cc=myfun, cc.args=list(a=2,b=15) ){
list(a=a, b=b, cc = function(x) cc(x, cc.args$a, cc.args$b))
}

mysecond.fun(a=1,b=2)$cc(x=12)

It may be that you're after a Curry (*) function, as in,

Curry <-  # from roxygen
function (f, ..., .left=TRUE)
{
    .orig = list(...)
    function(...){
    if(.left) {args <- c(.orig, list(...))} else {args <- c(list(...),
.orig)}
     do.call(f, args)
    }
}

I believe there are some recent discussions on currying in the archives.

(*): http://en.wikipedia.org/wiki/Currying


HTH,

baptiste





2009/6/26 Miguel Bernal <mbernal@marine.rutgers.edu>
> Dear R-users,
>
> I am trying to develop a function that takes another function as an
> argument,
> changes its default values and returns a list of things, among which the
> initial function with its default arguments changed. An example of what i
> will like to obtain below:
>
> ## initial function
>
> myfun <- function(x, a=19, b=21){ return(a * x + b) }
>
> ## this is the function i will like to create
> ## (does not work as it is written here)
>
> mysecond.fun <- function(a, b, c = myfun(a=2, b=15)){
> return(list(a=a, b=b c=c))
> }
>
> So I would be able to call:
>
> mysecond.fun$c(x=12)
>
> And this will be equivalent of calling:
>
> myfun(x=12, a=2, b=15 ) ## i.e. i have changed the default values of myfun
> and
>                        ## stored it in a new function mysecond.fun$c
>
> Any help will be greatly appreciated!
>
> Miguel Bernal.
>
>
> ----
> Current address:
> Ocean Modeling group,
> Institute of Marine and Coastal Sciences
> University of Rutgers
> 71 Dudley Road, New Brusnkwick,
> New Jersey 08901, USA
> email: mbernal@marine.rutgers.edu
> phone: +1 732 932 3692
> Fax: +1 732 932 8578
> ---------------------------------------------
> Permanent address:
> Instituto Español de Oceanografía
> Centro Oceanográfico de Cádiz
> Puerto Pesquero, Muelle de Levante, s/n
> Apdo. 2609, 11006 Cádiz, Spain
> email: miguel.bernal@cd.ieo.es
> phone: +34 956 294189
> Fax: +34 956 294232
>
> ______________________________________________
> R-help@r-project.org 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.
>


-- 

_____________________________

Baptiste Auguié

School of Physics
University of Exeter
Stocker Road,
Exeter, Devon,
EX4 4QL, UK

Phone: +44 1392 264187

http://newton.ex.ac.uk/research/emag
______________________________

	[[alternative HTML version deleted]]

Look at the source code to the Defaults package.

On Fri, Jun 26, 2009 at 12:52 PM, Miguel
Bernal<mbernal at marine.rutgers.edu> wrote:
> Dear R-users,
>
> I am trying to develop a function that takes another function as an
argument,
> changes its default values and returns a list of things, among which the
> initial function with its default arguments changed. An example of what i
> will like to obtain below:
>
> ## initial function
>
> myfun <- function(x, a=19, b=21){ return(a * x + b) }
>
> ## this is the function i will like to create
> ## (does not work as it is written here)
>
> mysecond.fun <- function(a, b, c = myfun(a=2, b=15)){
> return(list(a=a, b=b c=c))
> }
>
> So I would be able to call:
>
> mysecond.fun$c(x=12)
>
> And this will be equivalent of calling:
>
> myfun(x=12, a=2, b=15 ) ## i.e. i have changed the default values of myfun
and
> ? ? ? ? ? ? ? ? ? ? ? ?## stored it in a new function mysecond.fun$c
>
> Any help will be greatly appreciated!
>
> Miguel Bernal.
>
>
> ----
> Current address:
> Ocean Modeling group,
> Institute of Marine and Coastal Sciences
> University of Rutgers
> 71 Dudley Road, New Brusnkwick,
> New Jersey 08901, USA
> email: mbernal at marine.rutgers.edu
> phone: +1 732 932 3692
> Fax: +1 732 932 8578
> ---------------------------------------------
> Permanent address:
> Instituto Espa?ol de Oceanograf?a
> Centro Oceanogr?fico de C?diz
> Puerto Pesquero, Muelle de Levante, s/n
> Apdo. 2609, 11006 C?diz, Spain
> email: miguel.bernal at cd.ieo.es
> phone: +34 956 294189
> Fax: +34 956 294232
>
> ______________________________________________
> R-help at r-project.org 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.
>