[R] help in substitute function

Gabor Grothendieck ggrothendieck at gmail.com
Fri Oct 5 15:53:17 CEST 2007

```Given this:

x1 <- "pred"
x2 <- "lat"
e <- expression(1+2*pred+3*lat)

Try this:

L <- list(as.name("x1"), as.name("x2"))
names(L) <- c(x1, x2)
do.call(substitute, list(e, L)) # e & L are evaluated first

or perhaps:

f <- e
f <- sub("pred", "x1", f) # also converts to character
f <- sub("lat", "x2", f)
parse(text = sub("lat", "x2", f)) # convert back to expression

On 10/5/07, Ronaldo Reis Junior <chrysopa at gmail.com> wrote:
> Hi,
>
> I try to use a substitute function to generalise a equation.
>
> I have this:
>
> expression(1+2*pred+3*lat)
>
> I need to define the equation in function of x1 and x2 variables. Also I try
> to define who is x1 and x2. I try this:
>
> X1 <- "pred"
> X2 <- "lat"
>
> Now I need substitute pred and lat in equation by x1 and x2 defined on X1 and
> X2 above, I try this way:
>
> >
> substitute(expression(1+2*pred+3*lat),list(as.name(X1)=as.name(x1),as.name(X2)=as.name(x2))
> Error: unexpected '='
> in "substitute(expression(1+2*pred+3*lat),list(as.name(X1)="
>
> My expected result is:
>
> expression(1 + 2 * x1 + 3 * x2)
>
> Any help?
> Thanks
> Ronaldo
> --
> > Prof. Ronaldo Reis Júnior
> |  .''`. UNIMONTES/Depto. Biologia Geral/Lab. de Biologia Computacional
> | : :'  : Campus Universitário Prof. Darcy Ribeiro, Vila Mauricéia
> | `. `'` CP: 126, CEP: 39401-089, Montes Claros - MG - Brasil
> |   `- Fone: (38) 3229-8187 | ronaldo.reis at unimontes.br | chrysopa at gmail.com
> | http://www.ppgcb.unimontes.br/ | ICQ#: 5692561 | LinuxUser#: 205366
>
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