警告（）在函数内不起作用？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 

警告的数量应该是1而不是0 - 看起来warnings()在函数内调用时不会返回任何内容。为什么？如果发生警告，如何解决这个问题以检查函数，并将其打印出来？

我不想使用tryCatch，因为那时我失去了该函数返回的值（它可能仍然会返回一个有效值，即使它产生了警告）。

Answer 1

下面是suppressWarnings

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

我已经调整了它一点点的代码请计数警告的数量。

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 

另一项测试：

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

Answer 2

你的例子确实返回一个警告。

> 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! 

文档不明确的，但我不认为last.warning被置位，直到调用完成（特别是考虑到该呼叫是可以返回哪一部分）。

Answer 3

可能这是一个非常非常糟糕的解决办法...

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() 

调用该函数两次，如果出现警告...... 虽然我相信一定有更优雅的解决方案

Answer 4

的警告是不在函数返回之前发出。 见选项的文档（ “警告”）：

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

Answer 5

这里是一个解决办法

..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 
>