[R] object not found inside function

[Uwe Ligges]

Maria Montez wrote:
> Hi!
> 
> When running the following code I get the message: Error in eval(expr, 
> envir, enclos) : object "A" not found
> 
> fm <- function(p,ydata, env = parent.frame()) {
> #fit model y ~ (b0+b1x1+...+bpxp)*exp(g2plus*z2plus) where bi and g2plus 
> are parameters
> 
>   #create design matrix for linear part
>   fo00 <- paste("~",paste(paste("x",1:p,sep=""),collapse="+"),sep="")
>   fo0 <- as.formula(fo00)
>   A <- model.matrix(fo0,data=ydata)
> 
>  # create z variable
>   z2plus <- ifelse(totx>1,1,0)
>   ydata <- data.frame(ydata,z2plus)
> 
>  #run model
>   t2 <- nls(y ~ 
> A*exp(g2plus*z2plus),data=ydata,start=c(g2plus=0),alg="plinear")
> }
> model <- fm(4,ydata)
> 
> The code inside the function works if not enclosed in a function. This 
> makes me think that it is a scope problem and I need to specify the 
> environment. Even though I've read about environment and lexical scope I 
> still don't fully understand how it works. Sometimes I can do it others 
> I can't!
> 
> Can someone help me?
> 
> I've included below code to create a dataframe that can be used to test 
> my code.
> 
> Thanks, Maria
>

[data deleted]

Maria,

1. Do you really want to paste() the formula fo0 together that way?
2. For me, the functions fails because totx is not known. Please make 
sure to post *reproducible* code (OK, you almost did).
3. If totx is known, the function works for me, hence I guess you are 
using an outdated version (< 2.5.0) of R. --> Please always specify the 
version of R and the OS you are using.

Uwe