How to catch both warnings and errors?

On Dec 5, 2010, at 3:13 PM, Marius Hofert wrote:

Dear expeRts,

I am struggling with warning/error handling.

I would like to call a function which can produce either
a) normal output
b) a warning
c) an error

Since the function is called several (thousand) times in a loop, I would like
to proceed "quietly" and collect the warnings and errors [to deal with them at a
later point].

I do not see the function warnings() being used below:

?warnings

It delivers the stored warnings with different default behavior for interactive and non-interactive sessions.

I have seen constructs with tryCatch (which can deal with errors) and with
withCallingHandlers (which can deal with warnings), but I cannot figure out how
to catch *both* warnings and errors. Below is a minimal example of the function
that is called several times in a large loop. The function should catch warnings
and errors; the former work fine, but with the latter I do not know how to proceed.

Made some changes in you code but don't know if it is what you were hoping for:

f <- function(x){
  ## warnings
  w.list <- NULL # init warning
  w.handler <- function(w){ # warning handler
	    warn <- simpleWarning(w$message, w$call) # build warning
# first change here
      w.list <<- c(w.list, paste(warnings(), collapse = " ")) # save warning
      invokeRestart("muffleWarning")
      }
  ## errors
    e.list <- NULL # init errors   # not sure this is  good idea
    e.handler <- function(e){ # error handler
	     err <- c(e.list, e$message, e$call) # save error
	     return( err)
       }
  ## execute command
# wrapped cal in try()
  res <- withCallingHandlers(try(log(x)), warning = w.handler, error = e.handler)
  ## return result with warnings and errors
  list(result = res, warning = w.list, error = e.list)
}

f(-1) 

f("a")