default values

Thanks a lot.

You were right :-)

Professor Ripley can I use your SPLUS book for R too ?

2008/3/12, Prof Brian Ripley <ripley at stats.ox.ac.uk>:

On Wed, 12 Mar 2008, Dwayne Blind wrote:

Dear R users,

I wrote the following toy example to explain my problem :

a=0
f=function(x,y,z) {
   if (a==0) x[1]+x[2]+y
   if (a!=0) x[1]+x[2]+y+z
}
f(1:2,3)


I have not specified z and I get an error.

What was the error?  It works for me (so I've no idea), and returns NULL,
the value of the last expression (invisibly).  I think you intended

f <- function(x, y, z) if (a==0) x[1]+x[2]+y else x[1]+x[2]+y+z

or

f <- function(x, y, z) ifelse(a==0, x[1]+x[2]+y, x[1]+x[2]+y+z)

Although a=0, R seems to want to
know z because it's in the expression x[1]+x[2]+y+z.

So I tried to put a default value :

a=0
f=function(x,y,z=0) {
   if (a==0) x[1]+x[2]+y
   if (a!=0) x[1]+x[2]+y+z
}
f(1:2,3)

Why isn't it working ? Sometimes everything is fine even though a

parameter

is not specified.

Thanks a lot.

      [[alternative HTML version deleted]]