Given the following R knitr document:
\documentclass{article}
\begin{document}
<<data>>=
opts_chunk$set(comment = NA) # omits "##" at beginning of error message
x <- data.frame(x1 = 1:10)
y <- data.frame()
#
<<output_x>>=
if (nrow(x) == 0) stop("x is an empty data frame.") else summary(x)
#
<<output_y>>=
if (nrow(y) == 0) stop("y is an empty data frame.") else summary(y)
#
\end{document}
As expected, the last chunk returns an error with the custom message. The compiled PDF looks a little different:
Error: y is an empty data frame.
I want this text to just be
y is an empty data frame.
Without the Error: part or the red color. Can I achieve this? How?
Edit: I was able to make it in the mock data through the following workaround:
<<output_y>>=
if (nrow(y) == 0) cat("y is an empty data frame.") else summary(y)
#
However, that doesn't work with my real data, because I need the function to be stopped at that point.
Although I do not understand why an error should not be called Error, you are free to customize the output hook error to remove Error: from the message:
library(knitr)
knit_hooks$set(error = function(x, options) {
knitr:::escape_latex(sub('^Error: ', '', x))
})
You could do something like this. options("show.error.messages" = FALSE) turns off error messages, so you could temporarily employ that once the if statement is entered and use on.exit to reset it.
This way, stop stops the function, Error: is avoided, and the desired message is printed in red.
> f <- function(x) {
if(x > 5) {
g <- getOption("show.error.messages")
options(show.error.messages = FALSE)
on.exit(options(show.error.messages = g))
message("x is greater than 5.")
stop()
}
x
}
> f(2)
# [1] 2
> f(7)
# x is greater than 5.
Note: I'm not exactly sure how safe this is and I'm not a big supporter of changing options settings inside functions.
Related
I'm trying to find a place of the warning in the function:
fun <- function(x, y){
z = sum(x,y)
if(z > 15)
warning("Potential problem")
return(z)
}
x = 10; y = 20
fun(x, y)
The result I'd like to get is the line number of the warning (not only warning msgs created by developer) and the function name where it exists. The name of a function I can get with the withCallingHandlers function, however I don't know how to find the line number of the warning.
|function_name | warning_index |
--------------------------------
|fun |4 |
EDITED to use base functions:
You can use sys.calls() to see the call stack, and then look through it for lines with debug info. Here's a demonstration that does it.
# First, some code that will generate a warning
fun <- function(x, y){
z = sum(x,y)
if(z > 15)
warning("Potential problem")
return(z)
}
x = 10; y = 20
# Here's a handler that looks through the call stack
# for locations. Not all calls have recorded locations
# (most packages are installed without debug info)
# but this will find the debug info if it is there,
# and add it to the warning message.
locatedWarnings <- function(e) {
calls <- sys.calls()
locations <- character()
for (i in rev(seq_along(calls)))
if (!is.null(srcref <- getSrcref(calls[[i]])))
locations <- c(locations, sprintf("%s:%d", getSrcFilename(srcref), srcref[1]))
# If we found any locations, redo the warning
# with those locations prepended to the message
if (length(locations)) {
call <- if (!is.null(e$call)) paste("In", deparse(e$call)) else ""
warning(sprintf("%s at %s: %s", call, paste(locations, collapse=","), conditionMessage(e)), call. = FALSE)
invokeRestart("muffleWarning")
}
}
withCallingHandlers(fun(x, y),
warning = locatedWarnings)
#> Warning: In fun(x, y) at <text>:5: Potential problem
#> [1] 30
Created on 2023-02-15 with reprex v2.0.2
If you put this example in a file and source it with the default keep.source = TRUE, you'll get the filename and line for the warning line as well as the withCallingHandlers() line. Not sure why reprex didn't give the second one. If you just execute it by cut and paste to the console you won't get very useful line info, because every statement restarts the line count.
In R, how can I determine whether a function call results in a warning?
That is, after calling the function I would like to know whether that instance of the call yielded a warning.
If you want to use the try constructs, you can set the options for warn. See also ?options. Better is to use tryCatch() :
x <- function(i){
if (i < 10) warning("A warning")
i
}
tt <- tryCatch(x(5),error=function(e) e, warning=function(w) w)
tt2 <- tryCatch(x(15),error=function(e) e, warning=function(w) w)
tt
## <simpleWarning in x(5): A warning>
tt2
## [1] 15
if(is(tt,"warning")) print("KOOKOO")
## [1] "KOOKOO"
if(is(tt2,"warning")) print("KOOKOO")
To get both the result and the warning :
tryCatch(x(5),warning=function(w) return(list(x(5),w)))
## [[1]]
## [1] 5
##
## [[2]]
## <simpleWarning in x(5): A warning>
Using try
op <- options(warn=2)
tt <- try(x())
ifelse(is(tt,"try-error"),"There was a warning or an error","OK")
options(op)
On the R-help mailing list (see http://tolstoy.newcastle.edu.au/R/help/04/06/0217.html), Luke Tierney wrote:
"If you want to write a function that computes a value and collects all
warning you could do it like this:
withWarnings <- function(expr) {
myWarnings <- NULL
wHandler <- function(w) {
myWarnings <<- c(myWarnings, list(w))
invokeRestart("muffleWarning")
}
val <- withCallingHandlers(expr, warning = wHandler)
list(value = val, warnings = myWarnings)
}
2019 update
You can you use 'quietly' from the purrr package, which returns a list of output, result, warning and error. You can then extract each element by name. For instance, if you had a list, which you want to map a function over, and find the elements which returned a warning you could do
library(purrr)
library(lubridate)
datelist <- list(a = "12/12/2002", b = "12-12-2003", c = "24-03-2005")
# get all the everything
quiet_list <- map(datelist, quietly(mdy))
# find the elements which produced warnings
quiet_list %>% map("warnings") %>% keep(~ !is.null(.))
# or
quiet_list %>% keep(~ length(.$warnings) != 0)
For this example it's quite trivial, but for a long list of dataframes where the NAs might be hard to spot, this is quite useful.
here is an example:
testit <- function() warning("testit") # function that generates warning.
assign("last.warning", NULL, envir = baseenv()) # clear the previous warning
testit() # run it
if(length(warnings())>0){ # or !is.null(warnings())
print("something happened")
}
maybe this is somehow indirect, but i don't know the more straightforward way.
For a simple TRUE/FALSE return on whether a given operation results in a warning (or error), you could use the is.error function from the berryFunctions package, after first setting options(warn = 2) so that warnings are converted to errors.
E.g.,
options(warn = 2)
berryFunctions::is.error(as.numeric("x")) # TRUE
berryFunctions::is.error(as.numeric("3")) # FALSE
If you want to limit the option change to the use of this function, you could just create a new function as follows.
is.warningorerror <- function(x) {
op <- options()
on.exit(options(op))
options(warn = 2)
berryFunctions::is.error(x)
}
is.warningorerror(as.numeric("x")) # TRUE
options("warn") # still 0 (default)
I personally use the old good sink redirected into a text connection:
# create a new text connection directed into a variable called 'messages'
con <- textConnection("messages","w")
# sink all messages (i.e. warnings and errors) into that connection
sink(con,type = "message")
# a sample warning-generating function
test.fun <- function() {
warning("Your warning.")
return("Regular output.")
}
output <- test.fun()
# close the sink
sink(type="message")
# close the connection
close(con)
# if the word 'Warning' appears in messages than there has been a warning
warns <- paste(messages,collapse=" ")
if(grepl("Warning",warns)) {
print(warns)
}
# [1] "Warning message: In test.fun() : Your warning."
print(output)
# [1] "Regular output."
Possibly more straightforward and cleaner than the other suggested solutions.
I have a regression model (lm or glm or lmer ...) and I do fitmodel <- lm(inputs) where inputs changes inside a loop (the formula and the data). Then, if the model function does not produce any warning I want to keep fitmodel, but if I get a warning I want to update the model and I want the warning not printed, so I do fitmodel <- lm(inputs) inside tryCatch. So, if it produces a warning, inside warning = function(w){f(fitmodel)}, f(fitmodel) would be something like
fitmodel <- update(fitmodel, something suitable to do on the model)
In fact, this assignation would be inside an if-else structure in such a way that depending on the warning if(w$message satisfies something) I would adapt the suitable to do on the model inside update.
The problem is that I get Error in ... object 'fitmodel' not found. If I use withCallingHandlers with invokeRestarts, it just finishes the computation of the model with the warning without update it. If I add again fitmodel <- lm(inputs) inside something suitable to do on the model, I get the warning printed; now I think I could try suppresswarnings(fitmodel <- lm(inputs)), but yet I think it is not an elegant solution, since I have to add 2 times the line fitmodel <- lm(inputs), making 2 times all the computation (inside expr and inside warning).
Summarising, what I would like but fails is:
tryCatch(expr = {fitmodel <- lm(inputs)},
warning = function(w) {if (w$message satisfies something) {
fitmodel <- update(fitmodel, something suitable to do on the model)
} else if (w$message satisfies something2){
fitmodel <- update(fitmodel, something2 suitable to do on the model)
}
}
)
What can I do?
The loop part of the question is because I thought it like follows (maybe is another question, but for the moment I leave it here): it can happen that after the update I get another warning, so I would do something like while(get a warning on update){update}; in some way, this update inside warning should be understood also as expr. Is something like this possible?
Thank you very much!
Generic version of the question with minimal example:
Let's say I have a tryCatch(expr = {result <- operations}, warning = function(w){f(...)} and if I get a warning in expr (produced in fact in operations) I want to do something with result, so I would do warning = function(w){f(result)}, but then I get Error in ... object 'result' not found.
A minimal example:
y <- "a"
tryCatch(expr = {x <- as.numeric(y)},
warning = function(w) {print(x)})
Error in ... object 'x' not found
I tried using withCallingHandlers instead of tryCatch without success, and also using invokeRestart but it does the expression part, not what I want to do when I get a warning.
Could you help me?
Thank you!
The problem, fundamentally, is that the handler is called before the assignment happens. And even if that weren’t the case, the handler runs in a different scope than the tryCatch expression, so the handler can’t access the names in the other scope.
We need to separate the handling from the value transformation.
For errors (but not warnings), base R provides the function try, which wraps tryCatch to achieve this effect. However, using try is discouraged, because its return type is unsound.1 As mentioned in the answer by ekoam, ‘purrr’ provides soundly typed functional wrappers (e.g. safely) to achieve a similar effect.
However, we can also build our own, which might be a better fit in this situation:
with_warning = function (expr) {
self = environment()
warning = NULL
result = withCallingHandlers(expr, warning = function (w) {
self$warning = w
tryInvokeRestart('muffleWarning')
})
list(result = result, warning = warning)
}
This gives us a wrapper that distinguishes between the result value and a warning. We can now use it to implement your requirement:
fitmodel = with(with_warning(lm(inputs)), {
if (! is.null(warning)) {
if (conditionMessage(warning) satisfies something) {
update(result, something suitable to do on the model)
} else {
update(result, something2 suitable to do on the model)
}
} else {
result
}
})
1 What this means is that try’s return type doesn’t distinguish between an error and a non-error value of type try-error. This is a real situation that can occur, for example, when nesting multiple try calls.
It seems that you are looking for a functional wrapper that captures both the returned value and side effects of a function call. I think purrr::quietly is a perfect candidate for this kind of task. Consider something like this
quietly <- purrr::quietly
foo <- function(x) {
if (x < 3)
warning(x, " is less than 3")
if (x < 4)
warning(x, " is less than 4")
x
}
update_foo <- function(x, y) {
x <- x + y
foo(x)
}
keep_doing <- function(inputs) {
out <- quietly(foo)(inputs)
repeat {
if (length(out$warnings) < 1L)
return(out$result)
cat(paste0(out$warnings, collapse = ", "), "\n")
# This is for you to see the process. You can delete this line.
if (grepl("less than 3", out$warnings[[1L]])) {
out <- quietly(update_foo)(out$result, 1.5)
} else if (grepl("less than 4", out$warnings[[1L]])) {
out <- quietly(update_foo)(out$result, 1)
}
}
}
Output
> keep_doing(1)
1 is less than 3, 1 is less than 4
2.5 is less than 3, 2.5 is less than 4
[1] 4
> keep_doing(3)
3 is less than 4
[1] 4
Are you looking for something like the following? If it is run with y <- "123", the "OK" message will be printed.
y <- "a"
#y <- "123"
x <- tryCatch(as.numeric(y),
warning = function(w) w
)
if(inherits(x, "warning")){
message(x$message)
} else{
message(paste("OK:", x))
}
It's easier to test several argument values with the code above rewritten as a function.
testWarning <- function(x){
out <- tryCatch(as.numeric(x),
warning = function(w) w
)
if(inherits(out, "warning")){
message(out$message)
} else{
message(paste("OK:", out))
}
invisible(out)
}
testWarning("a")
#NAs introduced by coercion
testWarning("123")
#OK: 123
Maybe you could assign x again in the handling condition?
tryCatch(
warning = function(cnd) {
x <- suppressWarnings(as.numeric(y))
print(x)},
expr = {x <- as.numeric(y)}
)
#> [1] NA
Perhaps not the most elegant answer, but solves your toy example.
Don't put the assignment in the tryCatch call, put it outside. For example,
y <- "a"
x <- tryCatch(expr = {as.numeric(y)},
warning = function(w) {y})
This assigns y to x, but you could put anything in the warning body, and the result will be assigned to x.
Your "what I would like" example is more complicated, because you want access to the expr value, but it hasn't been assigned anywhere at the time the warning is generated. I think you'll have to recalculate it:
fitmodel <- tryCatch(expr = {lm(inputs)},
warning = function(w) {if (w$message satisfies something) {
update(lm(inputs), something suitable to do on the model)
} else if (w$message satisfies something2){
update(lm(inputs), something2 suitable to do on the model)
}
}
)
Edited to add:
To allow the evaluation to proceed to completion before processing the warning, you can't use tryCatch. The evaluate package has a function (also called evaluate) that can do this. For example,
y <- "a"
res <- evaluate::evaluate(quote(x <- as.numeric(y)))
for (i in seq_along(res)) {
if (inherits(res[[i]], "warning") &&
conditionMessage(res[[i]]) == gettext("NAs introduced by coercion",
domain = "R"))
x <- y
}
Some notes: the res list will contain lots of different things, including messages, warnings, errors, etc. My code only looks at the warnings. I used conditionMessage to extract the warning message, but
it will be translated to the local language, so you should use gettext to translate the English version of the message for comparison.
Here is my code:
test <- function(y){
irisname <- c("Sepal.Length","Sepal.Width","Petal.Length","Petal.Width","Species")
if(y %in% irisname){
print(y)
} else{
test <- function(...) stop("dummy error")
test(y)
}
}
> test("ds")
Error in test(y) : dummy error
In the result: "Error in test(y) : dummy error ", I need "ds" in test("ds"), not test(y).
How can I do that?
This almost does it (there's an extra colon ...), by using call.=FALSE to suppress the information about the call and hacking it into the error message.
update: added quotation marks to error #1; explained a bit more about why this problem is hard.
I don't know the structure of your code, but you are making life considerably harder for yourself by passing objects farther down into the structure. It would be a lot easier to call stop() directly from within your first level, or to use the information carried in y directly within your error message.
test <- function(y,stop=FALSE){
irisname <- c("Sepal.Length","Sepal.Width",
"Petal.Length","Petal.Width","Species")
if (stop) stop(sprintf("premature stop: var %s",y))
if(y %in% irisname){
print(y)
} else{
test <- function(...) {
stop(sprintf("in test(\"%s\"): dummy error",...),
call.=FALSE)
}
test(y)
}
}
test("junk")
## Error: in test("junk"): dummy error
test("junk",stop=TRUE)
## Error in test("junk", stop = TRUE) : premature stop: var junk
Getting rid of the spurious first colon in the output of test("junk") will be considerably harder, because the Error: string is hard-coded within R. Your best bet is probably, somehow, to print your own custom error message and then stop silently, or recreate the behaviour of stop() without generating the message (see ?condition: e.g. return(invisible(simpleError("foo")))). However, you're going to have to jump through a lot of hoops to do this, and it will be hard to ensure that you get exactly the same behaviour that you would have with stop() (e.g. will the error message have been saved in the error-message buffer?)
What you want to do is probably possible by mucking around with R internals enough, but in my opinion so hard that it would be better to rethink the problem ...
Good luck.
You could check the argument right at the start of the function. match.arg might come in handy, or you could print custom message and return NA.
two updates below
> test <- function(y)
{
if(!(y %in% names(iris))){
message(sprintf('test("%s") is an error. "%s" not found in string', y, y))
return(NA) ## stop all executions and exit the function
}
return(y) ## ... continue
}
> test("Sepal.Length")
# [1] "Sepal.Length"
> test("ds")
# test("ds") is an error. "ds" not found in string
# [1] NA
Add/Edit : Is there a reason why you're nesting a function when the function goes to else? I removed it, and now get the following. It seems all you are doing is checking an argument, and end-users (and RAM) want to know immediately if they enter an incorrect default arguments. Otherwise, you're calling up unnecessary jobs and using memory when you don't need to.
test <- function(y){
irisname <- c("Sepal.Length","Sepal.Width","Petal.Length","Petal.Width","Species")
if(y %in% irisname){
print(y)
} else{
stop("dummy error")
}
}
> test("ds")
# Error in test("ds") : dummy error
> test("Sepal.Length")
# [1] "Sepal.Length"
You could also use pmatch, rather than match.arg, since match.arg prints a default error.
> test2 <- function(x)
{
y <- pmatch(x, names(iris))
if(is.na(y)) stop('dummy error')
names(iris)[y]
}
> test2("ds")
# Error in test2("ds") : dummy error
> test2("Sepal.Length")
# [1] "Sepal.Length"
In R, how can I determine whether a function call results in a warning?
That is, after calling the function I would like to know whether that instance of the call yielded a warning.
If you want to use the try constructs, you can set the options for warn. See also ?options. Better is to use tryCatch() :
x <- function(i){
if (i < 10) warning("A warning")
i
}
tt <- tryCatch(x(5),error=function(e) e, warning=function(w) w)
tt2 <- tryCatch(x(15),error=function(e) e, warning=function(w) w)
tt
## <simpleWarning in x(5): A warning>
tt2
## [1] 15
if(is(tt,"warning")) print("KOOKOO")
## [1] "KOOKOO"
if(is(tt2,"warning")) print("KOOKOO")
To get both the result and the warning :
tryCatch(x(5),warning=function(w) return(list(x(5),w)))
## [[1]]
## [1] 5
##
## [[2]]
## <simpleWarning in x(5): A warning>
Using try
op <- options(warn=2)
tt <- try(x())
ifelse(is(tt,"try-error"),"There was a warning or an error","OK")
options(op)
On the R-help mailing list (see http://tolstoy.newcastle.edu.au/R/help/04/06/0217.html), Luke Tierney wrote:
"If you want to write a function that computes a value and collects all
warning you could do it like this:
withWarnings <- function(expr) {
myWarnings <- NULL
wHandler <- function(w) {
myWarnings <<- c(myWarnings, list(w))
invokeRestart("muffleWarning")
}
val <- withCallingHandlers(expr, warning = wHandler)
list(value = val, warnings = myWarnings)
}
2019 update
You can you use 'quietly' from the purrr package, which returns a list of output, result, warning and error. You can then extract each element by name. For instance, if you had a list, which you want to map a function over, and find the elements which returned a warning you could do
library(purrr)
library(lubridate)
datelist <- list(a = "12/12/2002", b = "12-12-2003", c = "24-03-2005")
# get all the everything
quiet_list <- map(datelist, quietly(mdy))
# find the elements which produced warnings
quiet_list %>% map("warnings") %>% keep(~ !is.null(.))
# or
quiet_list %>% keep(~ length(.$warnings) != 0)
For this example it's quite trivial, but for a long list of dataframes where the NAs might be hard to spot, this is quite useful.
here is an example:
testit <- function() warning("testit") # function that generates warning.
assign("last.warning", NULL, envir = baseenv()) # clear the previous warning
testit() # run it
if(length(warnings())>0){ # or !is.null(warnings())
print("something happened")
}
maybe this is somehow indirect, but i don't know the more straightforward way.
For a simple TRUE/FALSE return on whether a given operation results in a warning (or error), you could use the is.error function from the berryFunctions package, after first setting options(warn = 2) so that warnings are converted to errors.
E.g.,
options(warn = 2)
berryFunctions::is.error(as.numeric("x")) # TRUE
berryFunctions::is.error(as.numeric("3")) # FALSE
If you want to limit the option change to the use of this function, you could just create a new function as follows.
is.warningorerror <- function(x) {
op <- options()
on.exit(options(op))
options(warn = 2)
berryFunctions::is.error(x)
}
is.warningorerror(as.numeric("x")) # TRUE
options("warn") # still 0 (default)
I personally use the old good sink redirected into a text connection:
# create a new text connection directed into a variable called 'messages'
con <- textConnection("messages","w")
# sink all messages (i.e. warnings and errors) into that connection
sink(con,type = "message")
# a sample warning-generating function
test.fun <- function() {
warning("Your warning.")
return("Regular output.")
}
output <- test.fun()
# close the sink
sink(type="message")
# close the connection
close(con)
# if the word 'Warning' appears in messages than there has been a warning
warns <- paste(messages,collapse=" ")
if(grepl("Warning",warns)) {
print(warns)
}
# [1] "Warning message: In test.fun() : Your warning."
print(output)
# [1] "Regular output."
Possibly more straightforward and cleaner than the other suggested solutions.