R help - Sep 2006 - How to pass expression as an argument

Hi,
     I am writing a function and need to pass a function expression as an
argument,   for instance,
            myfun <-  function( express) {
                   x<- c(1,2,3)
                  y<-express
         }

    if I call the above function by myfun( x*2 ), I get  2  as the result, 
instead of  2,4,6 ,  could someone help me to
fix this problem ? 
    Furthermore,  is that possible to operate this expression on different
variables?  for example, in myfun(), I
might want to get  u*2,  z*2,  etc. without having to say x<-u, x<-z to
match the expression.

Thanks a lot for your help.

best

Tong Wang <wangtong at usc.edu> writes:
> Hi,
>      I am writing a function and need to pass a function expression as an
argument,   for instance,
>             myfun <-  function( express) {
>                    x<- c(1,2,3)
>                   y<-express
>          }
> 
>     if I call the above function by myfun( x*2 ), I get  2  as the result, 
instead of  2,4,6 ,  could someone help me to
> fix this problem ? 
>     Furthermore,  is that possible to operate this expression on different
variables?  for example, in myfun(), I
> might want to get  u*2,  z*2,  etc. without having to say x<-u, x<-z
to match the expression.
> 
> Thanks a lot for your help.
Either pass the expression explicitly using myfun(quote(x*2)) or
myfun(expression(x*2)) or use substitute(express) inside the function. 

-- 
   O__  ---- Peter Dalgaard             ?ster Farimagsgade 5, Entr.B
  c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
 (*) \(*) -- University of Copenhagen   Denmark          Ph:  (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)                  FAX: (+45) 35327907

On 27 Sep 2006 10:57:15 +0200, Peter Dalgaard <p.dalgaard at
biostat.ku.dk> wrote:
> Tong Wang <wangtong at usc.edu> writes:
>
> > Hi,
> >      I am writing a function and need to pass a function expression as
an argument,   for instance,
> >             myfun <-  function( express) {
> >                    x<- c(1,2,3)
> >                   y<-express
> >          }
> >
> >     if I call the above function by myfun( x*2 ), I get  2  as the
result,  instead of  2,4,6 ,  could someone help me to
> > fix this problem ?
> >     Furthermore,  is that possible to operate this expression on
different variables?  for example, in myfun(), I
> > might want to get  u*2,  z*2,  etc. without having to say x<-u,
x<-z to match the expression.
> >
> > Thanks a lot for your help.
>
> Either pass the expression explicitly using myfun(quote(x*2)) or
> myfun(expression(x*2)) or use substitute(express) inside the function.
>
Regarding the second option see the source of curve by entering:

curve