[R] formula in function as text?

[Berend Hasselman]

On 17-01-2012, at 13:36, Julia Burggraaf wrote:

> Hello all,
> 
> It might be a simple question, but I cannot find the solution, as I do not
> know which subjects I should search on. So, much thanks for he/she we can
> help me.
> I am creating a function and would like to place a formula in the function,
> without it being executed immediately. Like saving it temporary as 'text'.
> 
> Simplified version of what I would like to be able to do:
> 
> test<-function(a,x){
> if(a<5){ b<-3+ x[i]}
> if(a>5){ b<- 6 + x[i]}
> y<-1:10
> for (i in 1:10){y[i]<-4 + b}
> return(y)
> }
> 
> In my perfect world, R will replace b in the formula y=4+b by the
> appropriate b, indicated by the condition (value of a).
> It now takes for 'b' only the first argument of x (+3 or 6). I know I can
> solve the problem by also looping over b and turning it into a vector, but
> I would like to know if it is also possible in the way stated above. If I
> put 3+x[i] in "" to make it a character, it will still be character at
> y<-4+b or when I use as.numeric, it will create NA....


You are complicating matters.

test <- function(a,x){
	if(a<5){ b <- 3+ x} else if(a>5){ b<- 6 + x} # b is now a vector
        y <- 4 + b
       return(y)
}

Puzzle for you to solve: what happens when a is identical to 5?

Berend