使用tryCatch在R中加載數據文件

Question

我想要做的是從本地目錄加載數據文件。如果它不存在，請從網絡服務器下載。目前我正在使用嵌套tryCatch，它似乎工作。這是嘗試在R中完成此任務的正確方法嗎？

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

您可以使用函數file.exists(f)來查看文件是否存在。

當然也可能會出現其他錯誤，例如權限或文件格式問題，因此您可能希望將所有內容都包含在try-block中。