# [R] Elementary sapply question

Ajay Shah ajayshah at mayin.org
Mon Jun 21 20:57:30 CEST 2004

```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)
> >      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)
>  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

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