Question

处理R中的错误最好的是什么？我希望能够从我的脚本的最终用户中抽象出堆栈跟踪，以及清理我可能正在使用的任何临时变量和状态。

所以我想我的问题有两个方面：

最重要的是，在处理错误时如何正确处理清理状态？
如何在没有内部的情况下从R的错误消息中提取有用的好信息什么东西吐了？

目前，我有一些看起来像这样的东西，但是（1）它似乎非常不优雅，而且（2）仍然给我带来可怕的错误信息。

# Create some temporary working state and variables to clean up
file <- "somefile"
working.dir <- getwd()
setwd("../")  # Go somewhere else
saf.default <- getOption("stringsAsFactors")
options(stringsAsFactors = FALSE)

# Now lets try to open the file, but it doesn't work (for whatever reason)
# I want to clean up the state, stop, and wrap the error string with a nicer
# message
tryCatch({
  # Need to embed the tryCatch because we still need some of the state variables
  # for the error message
  tryCatch({
    f <- read.table(file)
  }, error = function(err.msg) {
    # Can't clean up here, we still need the `file variable!
    stop("Could not open file '", file, "' with error message:\n", print(err.msg), 
         call.=FALSE)
  })
}, error = function(err.msg) {
  # Now we can clean up state
  setwd(working.dir)
  options(stringsAsFactors = saf.default)
  rm(file, working.dir, saf.default, 
     envir=globalenv())  # This also seems awful?
  stop(print(err.msg), call.=FALSE)
})

# Do more stuff, get more state, handle errors, then clean up.
# I.e can't use `finally` in previous tryCatch!

来自此的错误消息显示为仍有许多丑陋的内部构件：

# <simpleError in file(file, "rt"): cannot open the connection>
# <simpleError: Could not open file 'somefile' with error message:
# Error in file(file, "rt"): cannot open the connection
>
# Error: Could not open file 'somefile' with error message:
# Error in file(file, "rt"): cannot open the connection
# In addition: Warning messages:
# 1: In file(file, "rt") :
#   cannot open file 'somefile': No such file or directory
# 2: In stop(print(err.msg), call. = FALSE) :
#   additional arguments ignored in stop()
>

Answer 1

我会将任何状态改变代码隔离到它自己的函数中，并使用on.exit。这可以保证无论发生错误都会发生清理。

readFile <- function(.....)
{
    on.exit({
        setwd(cur.dir)
        options(stringsAsFactors=saf)
    })
    cur.dir <- getwd()
    saf <- getOption("stringsAsFactors")
    setwd("new/dir")
    options(stringsAsFactors=FALSE)
    ....
}

当状态需要清理时，如何优雅地处理R中的错误？

1 个答案: