# [R] String mathematical function to R-function

Liaw, Andy andy_liaw at merck.com
Sun Jul 9 03:13:33 CEST 2006

```Here's one long-winded way of going about it, using R's ability to
manipulate functions as first class objects:

> f.string
[1] "x1 + sqrt(3*x2)"
> p.string <- parse(text=f.string)
> f <- function() {}        # empty function
> v <- all.vars(p.string)  # all the variables in the expression
> a <- do.call("alist", as.list(rep(TRUE, length(v)))) # contruct arguments
> names(a) <- v
> formals(f) <- a
> body(f) <- p.string
> f
function (x1 = TRUE, x2 = TRUE)
x1 + sqrt(3 * x2)
> f(3, 4)
[1] 6.464102

Andy

_____

From: r-help-bounces at stat.math.ethz.ch on behalf of Renaud Lancelot
Sent: Sat 7/8/2006 6:25 PM
To: Cleber N.Borges
Cc: r-help at stat.math.ethz.ch
Subject: Re: [R] String mathematical function to R-function [Broadcast]

> fun_String <- "-100*x1 + 0*x2 + 100*x3"
>
> fun <- function(x1, x2, x3){
+   eval(parse(text = fun_String))
+   }
>
> fun(4:0, -2:2, 0:4)
[1] -400 -200    0  200  400

Best,

Renaud

2006/7/8, Cleber N.Borges <klebyn at yahoo.com.br>:
>
>
> hello
>
> I make a subroutine that give-me a (mathematical)
> function in string format.
> I would like transform this string into function ( R
> function ).
>
> thanks for any tips.
> cleber
>
>
> #e.g.
> fun_String = "-100*x1 + 0*x2 + 100*x3"
>
> fun <- function(x1,x2,x3){
> return(
> ############
>
> evaluation( fun_String )
>
> ############
> )
>
>
>
>
>
> True String mathematical function :-(  :-(
>
> > nomes
> [1] "8.49*x1*z1 + 6.13*x1*z2 + 6.4*x1*z3 + 6.9*x2*z1 +
> 4.54*x2*z2 + 3.99*x2*z3 + 19.31*x3*z1 + 12.49*x3*z2 +
> 3.86*x3*z3 + 5.25*x1*z1*z2 + -6.2*x1*z1*z3 +
> 9.07*x1*z2*z3 + 10.87*x2*z1*z2 + 9.78*x2*z1*z3 +
> 49.05*x2*z2*z3 + 4.56*x1*x2*z1 + -4.9*x1*x2*z2 +
> 4.01*x1*x2*z3 + -0.39*x3*z1*z2 + 14.34*x3*z1*z3 +
> 0.7*x3*z2*z3 + -2.84*x1*x3*z1 + 20.25*x1*x3*z2 +
> 6.44*x1*x3*z3 + -4.91*x2*x3*z1 + 5.45*x2*x3*z2 +
> 37.99*x2*x3*z3 + -22.24*x1*z1*z2*z3 +
> -97.41*x2*z1*z2*z3 + -8.67*x1*x2*z1*z2 +
> 49.14*x1*x2*z1*z3 + 14.24*x1*x2*z2*z3 +
> 282.71*x3*z1*z2*z3 + 34.83*x1*x3*z1*z2 +
> 111.2*x1*x3*z1*z3 + 101.38*x1*x3*z2*z3 +
> -6.93*x2*x3*z1*z2 + 90.16*x2*x3*z1*z3 +
> -9.11*x2*x3*z2*z3 + 17.22*x1*x2*x3*z1 +
> -29.42*x1*x2*x3*z2 + -19.87*x1*x2*x3*z3 +
> -277.41*x1*x2*z1*z2*z3 + -482.82*x1*x3*z1*z2*z3 +
> -688.23*x2*x3*z1*z2*z3 + -588.4*x1*x2*x3*z1*z2 +
> -197.31*x1*x2*x3*z1*z3 + -722.58*x1*x2*x3*z2*z3 +
> 5536.59*x1*x2*x3*z1*z2*z3"
> >
>
>
>
>
>
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--
Renaud LANCELOT
Département Elevage et Médecine Vétérinaire (EMVT) du CIRAD
Directeur adjoint chargé des affaires scientifiques

CIRAD, Animal Production and Veterinary Medicine Department
Deputy director for scientific affairs

Campus international de Baillarguet
TA 30 / B (Bât. B, Bur. 214)
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