[R] Question regarding if statement in while loop

[Carl Witthoft]

Sounds like what you want is  either   try() or trycatch() -- check out 
the documentation.  Basically, putting your eblest() function inside a 
try() call allows you to return an error message if eblest crashes 
without crashing your main loop.

BTW,  for debugging purposes, I'd recommend creating a simple loop with 
an input some of whose values are guaranteed to cause a problem.  For 
example:

xin<-c(1,2,3,4,-5,6)

i<-1
while(i<=length(xin)){
sqrt(xin[i])
}


Carl


<original message follows>
I'm running R version 2.9.2 on a PC.

I'm having a problem with a loop, and have tried using an if statement 
within to fix it, but to no avail.
Any advice would be appreciated.

Here is my code:

eblest <- function(i,dir, sterr, weight, aux) { n <- nrow(dir)
Y <- as.matrix(dir[,i], ncol=1)
sigma2ei <- as.matrix(sterr[,i]^2, ncol=1)
w <- as.matrix((weight[,3])*(sigma2ei), ncol=1)
X <- as.matrix(subset(aux, select=c(3,5:7,9:10,13)))
a <<- EBLUP.area(Y,cbind(w,1),sigma2ei,n)            #The EBLUP.area
function is a function already in R.
}

               # It gives a bunch of output, some of what I need.

#THIS IS THE LOOP I'M HAVING A PROBLEM WITH: results <- 
data.frame(length=nrow(dir5)) i <- 3
while (i <=some number) {
eblest(i, dir5, sterr5, weight5, aux5)
out <<- cbind(i, a$EBLUP, a$mse)
results <- cbind(results, out)
i <- i+1
}

I have tried running the eblest function for a specific set of input (i, 
dir5, etc as in the function) This function runs ok. However, sometimes 
eblest does not create the expected output, sometimes due to the 
solution being singular or other reasons. I'm not so concerned about 
that at this point - it's a function of the data.

My problem is that, as you can see, after eblest runs, the "out" pieces 
of information are bound together in the results matrix. When the eblest 
does not run correctly, the loop stops.  For example, when i=3 and i=4, 
eblest runs ok, and I get a maxtrix with the following columns:

i EBLUP se.EBLUP i EBLUP se.EBLUP
3           x                y    4        a                bh


...but when it loops back around to start i=5, I get an error because 
the solution is singular. But I don't want the loop to stop (I have ~100 
of these i's for which I need to execute this function.

So I would like to set an if condition that will cause the loop to step 
ahead (in this case, to 6), and continue looping...Something like "if 
exists("out")=FALSE next, else..." However, when I tried that, the 
results matrix was empty created at all.

In case it helps, "out" has a "numeric" mode, and is a "matrix"...

I've written these functions and loops using online help and examples 
I've found on websites, but clearly I'm missing something.

Thanks for any help you can give!!