使用tryCatch将数据加载到R中

问题描述：

我要尝试的是从本地目录加载数据文件。如果不存在，请从网络服务器下载。目前，我正在使用嵌套的tryCatch，它似乎可以正常工作。这是尝试在R中完成该任务的正确方法吗？

What I am trying to do is load a data file from the local directory. If it is not there then download it from a webserver. Currently I am using a nested tryCatch and it appears to work. Is this the correct way to attempt to complete this task in R?

tryCatch( 
  {  
    #attempt to read file from current directory
    # use assign so you can access the variable outside of the function
    assign("installations", read.csv('data.csv'), envir=.GlobalEnv) 
    print("Loaded installation data from local storage")
  },
  warning = function( w )
  {
     print()# dummy warning function to suppress the output of warnings
  },
  error = function( err ) 
  {
    print("Could not read data from current directory, attempting download...")
    #attempt to read from website
    tryCatch(
    {
        # use assign so you can access the variable outside of the function
        assign("installations", read.csv('http://somewhere/data.csv'), envir=.GlobalEnv) 
        print("Loaded installation data from website")
    },
    warning = function( w )
    {
      print()# dummy warning function to suppress the output of warnings
    },
    error = function( err )
    {
      print("Could not load training data from website!! Exiting Program")
    })
  })

答

您可以使用函数 file.exists（f）来查看文件是否存在。

You can use the function file.exists(f) to see if a file exists.

当然，可能会发生其他错误，例如权限或文件格式问题，因此您可能还是希望将所有内容都包装在try块中。

Other errors may occur, of course, such as permissions or file format problems, so you might want to wrap everything in a try-block anyway.

使用tryCatch将数据加载到R中

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