使用tryCatch在R中加载数据文件

Question

我想要做的是从本地目录加载数据文件.如果不存在,则从网络服务器下载.目前我正在使用嵌套的tryCatch,它似乎工作.这是尝试在R中完成此任务的正确方法吗？

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")
    })
  })

Answer 1

您可以使用该函数file.exists(f)查看文件是否存在.

当然,可能会出现其他错误,例如权限或文件格式问题,因此您可能希望将所有内容都包装在try-block中.