[R] default values

[Prof Brian Ripley]

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]]
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595