warnings（）在函数中不起作用？如何解决这个问题？ [英] warnings() does not work within a function? How can one work around this?

问题描述

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 -
似乎在函数内调用 warnings（）不会返回任何东西。为什么？如果发生警告，可以如何检查功能，并打印出来？

Number of warnings should be 1 rather than 0 - it seems that warnings() returns nothing if called within a function. Why? How can one work around this to check within a function if warnings occurred, and print them out?

我不想使用 tryCatch ，因为我失去了函数返回的值（它可能仍然返回一个有效的值，即使它产生一个警告）。

I don't want to use tryCatch, because then I lose the value that the function returns (it may still return a valid value, even if it generated a warning).

推荐答案

以下是 suppressWarnings的代码

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

我已经调整了一点，以计算警告数。

I've tweaked it a little to count the number of warnings instead.

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
}

A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

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