[Rd] turning expression object to function

[Marc Schwartz]

On Mon, 2006-12-18 at 19:06 +0100, Antonio, Fabio Di Narzo wrote:
> Dear all,
> I have the following problem.
> 
> Given an expression object 'expr' containing a certain set of symbols
> (say 'a', 'b', 'c'), I would like to translate the expression object
> in an R function of, say, 'a', programmatically. Here an example of
> what I mean.
> 
> Given:
> > expr <- expression(a+b+c)
> 
> a call like:
> > asFunctionOf(expr, 'a', list(b=1, c=2))
> 
> should return a function (not necessarly formally) equivalent to
> > function(a) a+1+2
> 
> Some suggestions?
> 
> Best regards,
> Antonio.

Let me offer some pointers and a couple of possible examples:

?call
?as.function
?alist
?eval
?parse


expr <- expression(a + b + c)

> as.function(alist(a = , b = 1, c = 2, eval(expr)))(5)
[1] 8

> as.function(alist(a = , b = 1, c = 2, eval(expr)))(5, 10, 8)
[1] 23



MyExpr <- paste(letters[1:3], collapse = " + ")

> MyExpr
[1] "a + b + c"

> as.function(alist(a = , b = 1, c = 2, eval(parse(text = MyExpr))))(6)
[1] 9


HTH,

Marc Schwartz