如何检查函数调用是否导致警告?

如果你想使用 try 构造,可以设置警告选项。另见 ?options 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")

要同时获得结果和警告:

tryCatch(x(5),warning=function(w) return(list(x(5),w)))

## [[1]]
## [1] 5
## 
## [[2]]
## <simpleWarning in x(5): A warning>

使用

op <- options(warn=2)

tt <- try(x())
ifelse(is(tt,"try-error"),"There was a warning or an error","OK")
options(op)

在R-help邮件列表中(请参见 http://tolstoy.newcastle.edu.au/R/help/04/06/0217.html

“如果要编写一个计算值并收集所有 警告您可以这样做:

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)
} 

下面是一个例子:

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")
}

2019年更新

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)

对于这个例子来说,这很简单,但是对于NAs可能很难发现的一长串数据帧,这非常有用。