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)
}
The function should *always* return the list with the three
components.
How can I achieve this?
Cheers,
Marius
Ps: How can I get the warning/error message in a nice string (as it
is printed
in a normal warning/error message)? The approach shown below is
somehow ugly.
Basically, I had trouble converting the call w$call to a string.
## based on http://tolstoy.newcastle.edu.au/R/help/04/06/0217.html
## and http://www.mail-archive.com/r-help@r-project.org/msg81380.html
f <- function(x){
## warnings
w.list <- NULL # init warning
w.handler <- function(w){ # warning handler
warn <- simpleWarning(w$message, w$call) # build warning
w.list <<- c(w.list, paste(warn, collapse = " ")) # save
warning
invokeRestart("muffleWarning")
}
## errors
e.list <- NULL # init errors
e.handler <- function(e){ # error handler
err <- simpleError(e$message, e$call)
e.list <<- c(e.list, paste(err, collapse = " ")) # save error
}
## execute command
res <- withCallingHandlers(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(-1)
f("a")
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David Winsemius, MD
West Hartford, CT
______________________________________________
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
