On 10/22/2012 09:57 AM, luke-tier...@uiowa.edu wrote:
On Sun, 21 Oct 2012, Martin Morgan wrote:
On 10/21/2012 12:28 PM, Ben Bolker wrote:
Not desperately important, but nice to have and possibly of use to
others, is the ability to suppress specific warnings rather than
suppressing warnings indiscriminately. I often know of a specific
warning that I want to ignore (because I know that's it's a false
positive/ignorable), but the current design of suppressWarnings() forces
me to ignore *any* warnings coming from the expression.
I started to write a new version that would check and, if supplied
with a regular expression, would only block matching warnings and
otherwise would produce the warnings as usual, but I don't quite know
enough about what I'm doing: see ??? in expression below.
Can anyone help, or suggest pointers to relevant
examples/documentation (I've looked at demo(error.catching), which isn't
helping me ... ?)
suppressWarnings2 <- function(expr,regex=NULL) {
opts <- options(warn = -1)
on.exit(options(opts))
I'm not really sure what the options(warn=-1) is doing there, maybe its for
efficiency to avoid generating a warning message (as distinct from signalling
The sources in srs/library/base/conditions.R have
suppressWarnings <- function(expr) {
ops <- options(warn = -1) ## FIXME: temporary hack until R_tryEval
on.exit(options(ops)) ## calls are removed from methods code
withCallingHandlers(expr,
warning=function(w)
invokeRestart("muffleWarning"))
}
I uspect we have still not entirely eliminated R_tryEval in this context
but I'm not sure. Will check when I get a chance.
a warning). I think you're after something like
suppressWarnings2 <-
function(expr, regex=character())
{
withCallingHandlers(expr, warning=function(w) {
if (length(regex) == 1 && length(grep(regex, conditionMessage(w)))) {
invokeRestart("muffleWarning")
}
})
}
A problem with using expression matching is of course that this fails
with internationalized messages. Ideally warnings should be signaled as
warning conditions of a particular class, and that class can be used
to discriminate. Unfortunately very few warnings are designed this way.
Probably specific messages, rather than patterns, would be handled and then
suppressWarnings2 <- function(expr, messages = character())
{
opts <- options(warn = -1)
on.exit(options(ops))
withCallingHandlers(expr, warning=function(w) {
if (conditionMessage(w) %in% messages)
invokeRestart("muffleWarning")
})
}
gives one the illusion of speaking many languages
suppressWarnings2(log(-1), gettext("NaNs introduced", domain="R"))
Martin
Best,
luke
If the restart isn't invoked, then the next handler is called and the warning
is handled as normal. So with
f <- function() {
warning("oops")
2
}
there is
suppressWarnings2(f())
[1] 2
Warning message:
In f() : oops
suppressWarnings2(f(), "oops")
[1] 2
For your own code I think a better strategy is to create a sub-class of
warnings that can be handled differently
mywarn <-
function(..., call.=TRUE, immediate.=FALSE, domain=NULL)
{
msg <- .makeMessage(..., domain=domain, appendLF=FALSE)
call <- NULL
if (call.)
call <- sys.call(1L)
class <- c("silencable", "simpleWarning", "warning", "condition")
cond <- structure(list(message=msg, call=call), class=class)
warning(cond)
}
suppressWarnings3 <-
function(expr)
{
withCallingHandlers(expr, silencable=function(w) {
invokeRestart("muffleWarning")
})
}
then with
g <- function() {
mywarn("oops")
3
}
suppressWarnings3(f())
[1] 2
Warning message:
In f() : oops
g()
[1] 3
Warning message:
In g() : oops
suppressWarnings3(g())
[1] 3
withCallingHandlers(expr, warning = function(w) {
## browser()
if (is.null(regex) || grepl(w[["message"]],regex)) {
invokeRestart("muffleWarning")
} else {
## ? what do I here to get the warning issued?
## browser()
## computeRestarts() shows "browser",
## "muffleWarning", and "abort" ...
options(opts)
warning(w$message)
## how can I get back from here to the calling point
## *without* muffling warnings ... ?
}
})
}
suppressWarnings2(sqrt(-1))
suppressWarnings2(sqrt(-1),"abc")
It seems to me I'd like to have a restart option that just returns to
the point where the warning was caught, *without* muffling warnings ...
? But I don't quite understand how to set one up ...
Ben Bolker
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