R中的异常处理

Question

有人在R中有异常处理的示例/教程吗？官方文档非常简洁。

Answer 1

除了Shane的答案可以将您引向其他StackOverflow讨论之外，您还可以尝试使用代码搜索功能。此原始答案指向Google的代码搜索，此后已停止使用，但您可以尝试Github搜索，例如在此查询中以language = R 搜索tryCatch；Ohloh / Blackduck代码搜索，例如此查询R文件中的tryCatch在整个Debian档案库中的Debian代码搜索引擎只是为了记录在案，也有try，但tryCatch可能是可取的。我在Google代码搜索中尝试了一下快速计数，但是尝试为该动词本身获取了太多的误报-但它似乎tryCatch得到了更广泛的使用。

Answer 2

基本上，您想使用该tryCatch()功能。查看help（“ tryCatch”）了解更多详细信息。这是一个简单的示例（请记住，您可以执行任何您想做的错误操作）：vari <- 1tryCatch(print("passes"), error = function(e) print(vari), finally=print("finished"))&nbsp;tryCatch(stop("fails"), error = function(e) print(vari), finally=print("finished"))&nbsp;

Answer 3

该功能trycatch()相当简单，并且有很多很好的教程。在Hadley Wickham的书Advanced-R中可以找到R中错误处理的出色解释，其后的内容是一个非常基本的介绍，withCallingHandlers()并且withRestarts()用尽可能少的词：假设低级程序员编写了一个函数来计算绝对值。他不确定如何计算，但知道如何构造错误并努力传达自己的天真：low_level_ABS <- function(x){&nbsp; &nbsp; if(x<0){&nbsp; &nbsp; &nbsp; &nbsp; #construct an error&nbsp; &nbsp; &nbsp; &nbsp; negative_value_error <- structure(&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; # with class `negative_value`&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; class = c("negative_value","error", "condition"),&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; list(message = "Not Sure what to with a negative value",&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;call = sys.call(),&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;# and include the offending parameter in the error object&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;x=x))&nbsp; &nbsp; &nbsp; &nbsp; # raise the error&nbsp; &nbsp; &nbsp; &nbsp; stop(negative_value_error)&nbsp; &nbsp; }&nbsp; &nbsp; cat("Returning from low_level_ABS()\n")&nbsp; &nbsp; return(x)}一个中级程序员还编写了一个函数，使用可悲的不完整low_level_ABS函数来计算绝对值。他知道，negative_value 当的值为x负时，低级代码将引发错误，并通过建立允许用户控制错误恢复（或不恢复）的方式来建议解决问题的方法。restartmid_level_ABSmid_level_ABSnegative_valuemid_level_ABS <- function(y){&nbsp; &nbsp; abs_y <- withRestarts(low_level_ABS(y),&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; # establish a restart called 'negative_value'&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; # which returns the negative of it's argument&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; negative_value_restart=function(z){-z})&nbsp;&nbsp; &nbsp; cat("Returning from mid_level_ABS()\n")&nbsp; &nbsp; return(abs_y)}最终，高级程序员使用该mid_level_ABS函数来计算绝对值，并建立条件处理程序，该条件处理程序通过使用重新启动处理程序来告诉 错误mid_level_ABS从negative_value错误中恢复。high_level_ABS <- function(z){&nbsp; &nbsp; abs_z <- withCallingHandlers(&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; # call this function&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; mid_level_ABS(z) ,&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; # and if an `error` occurres&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; error = function(err){&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; # and the `error` is a `negative_value` error&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; if(inherits(err,"negative_value")){&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; # invoke the restart called 'negative_value_restart'&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; invokeRestart('negative_value_restart',&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;# and invoke it with this parameter&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;err$x)&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }else{&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; # otherwise re-raise the error&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; stop(err)&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; })&nbsp; &nbsp; cat("Returning from high_level_ABS()\n")&nbsp; &nbsp; return(abs_z)}所有这些的要点是，通过使用withRestarts()and withCallingHandlers()，该函数 high_level_ABS能够告诉您mid_level_ABS如何从错误引起的low_level_ABS错误中恢复而不会停止执行 mid_level_ABS，这是您无法做到的tryCatch()：> high_level_ABS(3)Returning from low_level_ABS()Returning from mid_level_ABS()Returning from high_level_ABS()[1] 3> high_level_ABS(-3)Returning from mid_level_ABS()Returning from high_level_ABS()[1] 3在实践中，low_level_ABS代表一个mid_level_ABS调用很多（甚至可能数百万次）的函数，针对错误的正确处理方法可能会因情况而异，如何处理特定错误的选择留给了更高级别的函数（high_level_ABS）。