[R] Trying to learn how to write a function... can't define a variable??

[William Dunlap]

Berend,
  The OP's ADD() is returning the new value of x, as do all
of your alternatives.  His problem is that he is not assigning
the output of ADD to a variable, as in
   z <- ADD(z)
Ordinary functions do not alter their arguments.   There is
no need for the 'x <-' in the definiton of ADD.  It may as
well be defined as 
  ADD <- function(x) x + 1

(One can write a replacement function, used as f(x)<-value,
that modifies its first argument, but that is a more advanced topic.)
  
Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com


> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf
> Of Berend Hasselman
> Sent: Friday, September 07, 2012 12:18 PM
> To: wwreith
> Cc: r-help at r-project.org
> Subject: Re: [R] Trying to learn how to write a function... can't define a variable??
> 
> 
> On 07-09-2012, at 20:00, wwreith wrote:
> 
> > I am just starting to experiment with writing a function and have run into
> > what seems like a limitation or more likely a lack of understanding on my
> > part.
> >
> > Very Simple Example:  I want to define a function that does 1+1=2.
> >
> > z<-1
> > ADD<-function(x)
> > {
> > x<-x+1
> > }
> > ADD(z)
> > z
> > output for z is 1 not the expected 2.
> >
> 
> expected ==> "desired"
> 
> Your ADD is not returning the new value of x.
> 
> Either
> 
> ADD<-function(x)
> {
> x<-x+1
> x  # return new value of x
> }
> 
> or
> 
> ADD<-function(x)
> {
> x<-x+1
> return(x)  # return new value of x
> }
> 
> or even
> 
> ADD<-function(x)
> {
> (x<-x+1)
> }
> 
> Have a look in the R-intro manual section "Writing your own functions"
> 
> Berend
> 
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