[R] from character string to function body?

[Atte Tenkanen]

Thanks Sundar!

I wonder that - when evaluating F1 - the right mathematical formula is now also printed!

> F1
function (x) 
x^3 + x^2 - 1

Atte

> 
> 
> Atte Tenkanen said the following on 7/7/2007 8:41 AM:
> > Dear R users,
> > 
> > I wonder if it is possible to form a function from a character 
> string. Here is an example:
> > 
> > 
> >> x=3
> >> `-`(`+`(`^`(x,3),`^`(x,2)),1) # Here is my function evaluated.
> > [1] 35
> > 
> >> V=list("`-
> `","(","`+`","(","`^`","(","x",",",3,")",",","`^`","(","x",",",2,")",")",",",1,")") # Here I construct the string, it could be vector as well?
> >>
> >> S=noquote(paste(V,collapse=""))
> >>
> >> S
> > [1] `-`(`+`(`^`(x,3),`^`(x,2)),1) # Here is the same as a 
> character string.
> > 
> > Now I'd like to create a function using this string, something 
> like this, but of course, this doesn't work:
> > 
> > S=as.expression(S)
> > 
> > F1<-function(x){S}
> > 
> > Is there some way to do this?
> > 
> > Cheers,
> > 
> > Atte Tenkanen
> > University of Turku, Finland
> > 
> > ______________________________________________
> > R-help at stat.math.ethz.ch 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.
> 
> How about:
> 
> V <- 
> list("`-
> `","(","`+`","(","`^`","(","x",",",3,")",",","`^`","(","x",",",2,")",")",",",1,")") 
> # Here I construct the string, it could be vector as well?
> S <- paste(V, collapse = "")
> 
> F1 <- function(x) {}
> body(F1) <- parse(text = S)
> F1(3)
> # [1] 35
> F1(2)
> # [1] 11
> 
> HTH,
> 
> --sundar
> 
>