[R] passing elements of named vector / named list to function

[Rainer M Krug]

Jeff Newmiller <jdnewmil at dcn.davis.ca.us> writes:

> It x is a list...
>
> do.call(fun,x)

Thanks - works perfectly. Only one further question:

In my original usage, fun() is an S3 Generic Function and takes as the
first argument an object which obviously *must not be* expanded, while
the ... need to be extended.

--8<---------------cut here---------------start------------->8---
fun.obj <- function(x, ...) {
  y <- fun2(x)
  y$text <- paste(y$text, ..., collapse="|")
  return(y)
}
--8<---------------cut here---------------end--------------->8---

so

--8<---------------cut here---------------start------------->8---
do.call(fun, c(x, list(A=2, B=3))
--8<---------------cut here---------------end--------------->8---

obviously does not work.

So at the moment I am using a helper function:

--8<---------------cut here---------------start------------->8---
x <- AClassObjObject()
funhelp <- function(...) {fun(x, ...)}
do.call(funhelp, list(A=2, B=3))
--8<---------------cut here---------------end--------------->8---

which works but is not nice at all (as the x is from the environment
below). Is there a way of expand the ... but not the x?

Thanks,

Rainer

>
> You should keep external data input away from this code construct to
> avoid intentional or unintentional misuse of your fun.
>
> If your toy example were your actual usage I would suggest the collapse argument of paste.
> ---------------------------------------------------------------------------
> Jeff Newmiller                        The     .....       .....  Go Live...
> DCN:<jdnewmil at dcn.davis.ca.us>        Basics: ##.#.       ##.#.  Live Go...
>                                       Live:   OO#.. Dead: OO#..  Playing
> Research Engineer (Solar/Batteries            O.O#.       #.O#.  with
> /Software/Embedded Controllers)               .OO#.       .OO#.  rocks...1k
> --------------------------------------------------------------------------- 
> Sent from my phone. Please excuse my brevity.
>
> On January 15, 2015 6:25:43 AM PST, Rainer M Krug <Rainer at krugs.de> wrote:
>>
>>Hi
>>
>>Following scenario: I have a function fun
>>
>>--8<---------------cut here---------------start------------->8---
>>fun <- function(A, B, C, ...){paste(A, B, C, ...)}
>>--8<---------------cut here---------------end--------------->8---
>>
>>and x defined as follow
>>
>>--8<---------------cut here---------------start------------->8---
>>x <- 1:5
>>names(x) <- LETTERS[x]
>>--8<---------------cut here---------------end--------------->8---
>>
>>now I want to pass the *elements* of x to fun as named arguments, i.e.
>>
>>,----
>>| > fun(A=1, B=2, C=3, D=4, E=5)
>>| [1] "1 2 3 4 5"
>>`----
>>
>>The below examples obviously do not work:
>>
>>,----
>>| > fun(x)
>>| Error in paste(A, B, C, list(...)) :
>>|   argument "B" is missing, with no default
>>| > fun(unlist(x))
>>| Error in paste(A, B, C, list(...)) :
>>|   argument "B" is missing, with no default
>>`----
>>
>>How can I extract from x the elements and pass them on to fun()?
>>
>>I could easily change x to a list() if this would be easier.
>>
>>--8<---------------cut here---------------start------------->8---
>>x <- list(A=1, B=2, C=3, D=4, E=5)
>>--8<---------------cut here---------------end--------------->8---
>>
>>In my actual program, x can have different elements as well as fun -
>>this is decided programmatically.
>>
>>Any suggestions how I can achieve this?
>>
>>Thanks,
>>
>>Rainer
>

-- 
Rainer M. Krug
email: Rainer<at>krugs<dot>de
PGP: 0x0F52F982
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