[R] avoid error within for loop, try, trycatch, while, move to next iteration, unlist

[William Dunlap]

You could put the try() into a while loop, inside for for or lapply loop,
as in:

> f <- function(x){ stopifnot(x>0.5) ; x }
> o <- numeric(100); for(i in seq_along(o)) { while(inherits(try(tmp <- f(runif(1)), silent=TRUE), "try-error")) {} ; o[[i]] <- tmp }
> range(o)
[1] 0.5000588 0.9991261

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com


> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf
> Of ?e???da? ?pa?t??
> Sent: Saturday, May 26, 2012 6:15 AM
> To: r-help at r-project.org
> Subject: [R] avoid error within for loop, try, trycatch, while, move to next iteration, unlist
> 
> 
> 
> 
> Hi there,
> 
> I would like to ask something about how to avoid a possible error message within a for
> loop. I am running a simulation and in some repetitions there may be an error that will
> cause a crash and stop the whole procedure, what I want is to simply move on to the
> next iteration automatically and discard the "bad" repetitions from my results. I used the
> "try" function to do this and it partially works.
> 
> Here is the thing:
> 
> logitsboots <- function(x,y,Jbh) {
> logitseb=0;logitspb=0;
> for (j in 1:1) {
> 
> 
> #some code here that has to do with random numbers that may or may not produce an
> error and calculates the values of two scalar quantities: spboots  and seboots,
> 
> 
>   logitspb=log(spboots/(1-spboots))
>   logitseb=log(seboots/(1-seboots))
> 
> #assume that I only care about logitseb for the moment
> }
> list(lse=logitseb)
> 
> }
> 
> 
> 
> # Now the following works just fine:
> 
> 
> res=0
> for(bb in 1:100) {
> res[bb] <- try(logitsboots(x,y,Jbh), TRUE)
>     }
> az=unlist(res[sapply(res, function(x) !inherits(x, "try-error"))])
> 
> 
> 
> 
> #So far, so good and everything is working fine with "az" having the values of lse having
> also discarded the "bad" iterations.
> 
> 
> However I would like to store (as an output) both values (logitse AND logitsp) in the
> function logitsboots, that is the list would be as :
> 
> 
> list(lse=logitseb,lsp=logitspb).
> 
> This way the quantity "res" would have two arguments: res$lse and res$lsp each time it is
> called. However when an error occures I just cannot seem to manage to "unlist" the "res"
> properly since typing "res$lse" for example will warn me that the "$" operator will not
> work (since it is not numeric anymore I guess). Something like the following would fail,
> but I guess that clears what I want to do.
> 
> 
> az1=unlist(res$lse[sapply(res$lse, function(x) !inherits(x, "try-error"))])
> 
> az2=unlist(res$lsp[sapply(res$lsp, function(x) !inherits(x, "try-error"))])
> 
> My final goal is to obtain 100 values of lse and 100 values of lsp. (Of course since the
> iterations leading to an error would be discarded I will end up with less than 100
> iterations. Any ideas of also using the "while" here in combination with the "try" to just
> discard the bad iterations and replace them with new good ones would be great. This
> way I would actually get exactly 100 values of lse and lsp).
> 
> Most important is to manage to keep both values in a two column matrix or something. I
> hope I was clear enough..
> 
> 
> 
> Thanx in advance for any answers!
> 
> Leo.
> 	[[alternative HTML version deleted]]