警告（）在函數內不起作用？如何解決這個問題？

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 

警告的數量應該是1而不是0 - 看起來warnings()在函數內調用時不會返回任何內容。爲什麼？如果發生警告，如何解決這個問題以檢查函數，並將其打印出來？

我不想使用tryCatch，因爲那時我失去了該函數返回的值（它可能仍然會返回一個有效值，即使它產生了警告）。

Answer 1

下面是suppressWarnings

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

我已經調整了它一點點的代碼請計數警告的數量。

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 
} 

測試：

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

另一項測試：

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

Answer 2

你的例子確實返回一個警告。

> 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! 

文檔不明確的，但我不認爲last.warning被置位，直到調用完成（特別是考慮到該呼叫是可以返回哪一部分）。

Answer 3

可能這是一個非常非常糟糕的解決辦法...

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() 

調用該函數兩次，如果出現警告...... 雖然我相信一定有更優雅的解決方案

Answer 4

的警告是不在函數返回之前發出。 見選項的文檔（ 「警告」）：

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

Answer 5

這裏是一個解決辦法

..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 
>