警告（）在函数中不起作用？如何解决这个问题？

Question

op <- options(warn=0)  #although doesn't work for any value of warn
assign("last.warning", NULL, envir = baseenv())  
thisDoesntWork<- function() {
warning("HEY, this is definitely a warning!")
cat(paste("number of warnings:",length(warnings())))
}   
>thisDoesntWork()
Warning in thisDoesntWork() : HEY, this is definitely a warning!
number of warnings: 0

警告数应为 1 而不是 0 - 如果在函数中调用，warnings() 似乎什么也不返回。为什么？如何解决此问题以检查函数中是否出现警告并将其打印出来？

我不想使用tryCatch，因为那样我会丢失函数返回的值（它可能仍然返回有效值，即使它产生了警告）。

Answer 1

这是suppressWarnings的代码

function (expr) 
{
    withCallingHandlers(expr, warning = function(w) invokeRestart("muffleWarning"))
}

我对其进行了一些调整，以计算警告的数量。

countWarnings <- function(expr) 
{
    .number_of_warnings <- 0L
    frame_number <- sys.nframe()
    ans <- withCallingHandlers(expr, warning = function(w) 
    {
      assign(".number_of_warnings", .number_of_warnings + 1L, 
        envir = sys.frame(frame_number))
      invokeRestart("muffleWarning")
    })
    message(paste("No. of warnings thrown:", .number_of_warnings))
    ans
}

测试：

countWarnings(log(-1))
No. of warnings thrown: 1
[1] NaN

另一个测试：

foo <- function()
{
  warning("first warning!")
  warning("second warning!")
  warning("third warning!")
  invisible()
}
countWarnings(foo())
No. of warnings thrown: 3
NULL

Answer 2

您的示例确实返回警告。

> assign("last.warning", NULL, envir = baseenv())  
> thisDoesntWork <- function() {
+   warning("HEY, this is definitely a warning!")
+   cat(paste("number of warnings:",length(warnings())),"\n")
+ }
> thisDoesntWork()
number of warnings: 0 
Warning message:
In thisDoesntWork() : HEY, this is definitely a warning!
> warnings()  # HEY, here's your warning!!!
Warning message:
In thisDoesntWork() : HEY, this is definitely a warning!

文档并不明确，但我认为 last.warning 在调用完成之前不会被设置（特别是考虑到调用是可以返回的一部分）。

Answer 3

可能这是一个非常非常糟糕的解决方法......

fw<-function(){warning("warn...");return(99)}
fn<-function(){return(88)}

f<-function(){
    w<-0
    v<-NULL
    v<-tryCatch(fw(),warning=function(w){w})
    if("warning"%in%class(v)){
        w<-w+1 # e.g., count up the number of warning
        v<-fw()
    }
    print(v)

    v<-NULL
    v<-tryCatch(fn(),warning=function(w){w})
    if("warning"%in%class(v)){
        w<-w+1 # e.g., count up the number of warning
        v<-fn()
    }
    print(v)
}
f()

如果出现警告，则调用该函数两次... 虽然我相信一定有更优雅的解决方案

Answer 4

这里有一个解决方法

..my_warning <- 0L

thisDoesWork<- function(){
    assign("last.warning", NULL, envir = baseenv())  
    warning("HEY, this is definitely a warning!", {..my_warning <<- ..my_warning+1L;""})
    str(last.warning)
    cat(paste("number of warnings:", ..my_warning, "\n"))
}


thisDoesWork()
Warning in thisDoesWork() : HEY, this is definitely a warning!
NULL
number of warnings: 1 
>     thisDoesWork()
Warning in thisDoesWork() : HEY, this is definitely a warning!
NULL
number of warnings: 2 
>     thisDoesWork()
Warning in thisDoesWork() : HEY, this is definitely a warning!
NULL
number of warnings: 3 
> 

Answer 5

警告不会在函数返回之前发出。 请参阅有关选项（“警告”）的文档：

options(warn=1L)
thisDoesntWork()
#Warning in thisDoesntWork() : HEY, this is definitely a warning!
#number of warnings: 1