打印在for循环中引发错误的列表项，并继续下一个列表项 [英] Print list item that throws error in for loop, and continue with next list item

问题描述

我正在尝试使长列表中的哪个文件引发错误更加清晰。我试过将 for 循环包装在 tryCatch（）中，但是我无法获得寻找。我要寻找的结果是：如果文件 i 抛出错误 sprintf（错误：％s出现格式问题，i）。

I'm trying to add some clarity to which file in a long list is throwing an error. I've tried wrapping the for loop in tryCatch(), but I can't get the behavior I'm looking for. The result I'm going for is: if file i throws an error sprintf("Error: %s has a formatting problem", i).

下面，我们创建一个包含三个文件的目录，其中两个文件应该由正确地读入列表， c >循环，这将引发错误，因为它是 xlsx 文件。

Below, we create a directory with three files, two of which should be read correctly into a list by the for loop, one which will throw an error because it's a xlsx file.

请注意，以下代码将创建并删除目录和三个文件

dir.create("Demo999")
setwd("Demo999")

write.csv(mtcars,"mtcars.csv")
xlsx::write.xlsx(mtcars,"mtcars.xlsx")
write.csv(mtcars,"mtcars2.csv")


files <- list.files()
data <- list()

for (i in files){
    f <- read.csv(i)
    data[[i]] <- f

}

# clean up generated files

setwd("..")
unlink("Demo999", recursive= TRUE, force= TRUE)

我想要的输出是：

错误：mtcars.xlsx出现格式问题。

"Error: mtcars.xlsx has a formatting problem."

此代码无法运行，但是 tryCatch 块的示例：

This code does not run, but is a sample tryCatch block:

tryCatch({
  for (i in files){
    f <- read.csv(i)
    data[[i]] <- f
  }
}, error = function() sprintf("Error: %s has a formatting problem", i))

推荐答案

将 tryCatch 放入循环内，而不是在循环之外。您不想尝试整个循环，如果循环失败，请执行其他操作；您希望循环尝试每个列表元素，并在失败时显示错误。这样，您可以返回并仅尝试重新尝试失败的文件。尝试以下操作：

Put the tryCatch inside the loop, not outside the loop. You don't want try the whole loop, and do something else if the loop fails; you want the loop to try each list element, and print an error if it fails. This way you can go back and re-attempt only the failed files. Try this:

for (i in files){
    tryCatch({
      f <- read.csv(i)
      data[[i]] <- f
      },
      error = function(e) print(sprintf("Error: %s has a formatting problem", i))
    )
}
# [1] "Error: mtcars.xlsx has a formatting problem"

names(data)
# [1] "mtcars.csv"  "mtcars2.csv"

请注意，在此示例中，您知道名称（数据）成功的原因，因此您可以轻松找到失败= setdiff（文件，名称（数据））。

Note that, in this nice example, you know what succeeded from the names(data), so you can easily find fails = setdiff(files, names(data)).

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