[R] how to use try()

[Sundar Dorai-Raj]

r.ghezzo wrote:

> Hello, I have a program with this section:
> ..
> for(i in 1:20){
>   lo <- nls(y~y0+a/(1+(x/x0)^b),start=list(y0=0.1,a=a0,x0=x00,b=-8.1))
>   beta[i] <- lo$m$getPars()[4]
> }
> ..
> If the fit works this is OK but if the fit fails, the whole program 
> fails so:
> ..
> for(i in 1:20){
>   try(lo <- nls(y~y0+a/(1+(x/x0)^b),start=list(y0=0.1,a=a0,x0=x00,b=-8.1)))
>   beta[i] <- lo$m$getPars()[4]
> }
> ..
> but the try catches the error in nls and beta[i] gets assigned beta[i-1] 
> from the previous loop. This is bad but no so bad as it can be checked,
> Now in some cases the error is in i=1 and the program stops!!
> is there a way to set lo$m$getPars() to zero before the call?
> I tried to understand the use of tryCatch() but frankly it is above me. 
> Sorry
> Thanks for any help
> Heberto Ghezzo
> Meakins-Christie Labs
> 

How about:

beta[i] <- if(data.class(lo) == "Error") 0 else lo$m$getPars()[4]

-sundar