[R] Elementary sapply question

[Ajay Shah]

I had asked:
  > > My problem is this. Suppose I have:
  > >      pythagorean <- function(x, y) {
  > >        return(x*x + y*y)
  > >      }
  > > 
  > > then how do I utilise sapply to replace
  > >      fixed.x = 3
  > >      y.values = c(3,4,5)
  > >      answers=numeric(3)
  > >      for (i in 1:3) {
  > >          answers[i] = pythagorean(fixed.x, y.values[i])
  > >      }

On Mon, Jun 21, 2004 at 02:49:48PM -0400, Liaw, Andy wrote:
> At least two ways:
> 
> 1. Use extra argument in the function being sapply()'ed; e.g.,
> 
> > f <- function(x, y) x*x + y*y
> > x <- 3:5
> > sapply(x, f, 3)
> [1] 18 25 34
> 
> [See the "..." argument in ?sapply.]

I am aware of the "..." in sapply(). I am unable to understand how
sapply will know where to utilise the x[i] values: as the 1st arg or
the 2nd arg for f(x, y)?

That is, when I say:

     sapply(x, f, 3)

how does sapply know that I mean:

    for (i in 3:5) {
        f(i, 3)
    }

and not

    for (i in 3:5) {
        f(3, i)
    }

How would we force sapply to use one or the other interpretation?

Thanks,

        -ans.

-- 
Ajay Shah                                                   Consultant
ajayshah at mayin.org                      Department of Economic Affairs
http://www.mayin.org/ajayshah           Ministry of Finance, New Delhi