R help - Aug 2007 - Evaluating f(x(2,3)) on a function f<- function(a,b){a+b}

Dear list
I have a function and a vector, say
    f <- function(a,b){a+b}
    x <- c(2,3)
I want to "evaluate f on x" in the sense of computing f(x[1],x[2]). I
would like it to be so that I can write f(x). (I know I can write a wrapper
function g <- function(x){f(x[1],x[2])}, but this is not really what I am
looking for). Is there a general way doing this (programmatically)? (E.g. by
"unpacking" the elements of x and putting them in the "right
places" when calling f...)
I've looked under formals, alist etc. but so far without luck.
 
Regards
Søren
 

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On 8/22/07, S?ren H?jsgaard <Soren.Hojsgaard at agrsci.dk>
wrote:
> I have a function and a vector, say
>     f <- function(a,b){a+b}
>     x <- c(2,3)
> I want to "evaluate f on x" in the sense of computing
f(x[1],x[2]). I would like it to be so that I can write f(x). (I know I can
write a wrapper function g <- function(x){f(x[1],x[2])}, but this is not
really what I am looking for). Is there a general way doing this
(programmatically)? (E.g. by "unpacking" the elements of x and putting
them in the "right places" when calling f...)
> I've looked under formals, alist etc. but so far without luck.
I hope that the following helps:
> f <- function(x) {sum(x)}
> f(c(2,3))
[1] 5
> f(c(2,3,5))
[1] 10
>
Paul

Try this:

do.call(f, as.list(x))

On 8/22/07, S?ren H?jsgaard <Soren.Hojsgaard at agrsci.dk>
wrote:
> Dear list
> I have a function and a vector, say
>    f <- function(a,b){a+b}
>    x <- c(2,3)
> I want to "evaluate f on x" in the sense of computing
f(x[1],x[2]). I would like it to be so that I can write f(x). (I know I can
write a wrapper function g <- function(x){f(x[1],x[2])}, but this is not
really what I am looking for). Is there a general way doing this
(programmatically)? (E.g. by "unpacking" the elements of x and putting
them in the "right places" when calling f...)
> I've looked under formals, alist etc. but so far without luck.
>
> Regards
> S?ren
>
>
>        [[alternative HTML version deleted]]
>
>
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