[R] How to pass expression as an argument

[Peter Dalgaard]

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. 

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