how to use try()

"r.ghezzo" <heberto.ghezzo at mcgill.ca> writes:

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

Just check the return value from try:

beta[i] <- if(inherits(try(.....),"try-error")) NA else lo$etc...

(or use sapply) and, er, shouldn't there be a dependency on i
somewhere in the model fit???