在R中调试意外错误-如何找到错误发生的地方? [英] Debugging unexpected errors in R -- how can I find where the error occurred?

问题描述

有时R会向我抛出诸如以下错误

Sometimes R throws me errors such as

if(ncol(x)！= 2){:参数长度为零

Error in if (ncol(x) != 2) { : argument is of length zero

在没有编写任何代码的情况下，没有其他信息.是否有找到在哪个程序包中哪个函数会导致错误的通用方法?

with no additional information, when I've written no such code. Is there a general way for finding which function in which package causes an error?

由于大多数程序包都经过压缩，因此对grep /usr/lib/R/library而言并非易事.

Since most packages come compressed, it isn't trivial to grep /usr/lib/R/library.

推荐答案

您可以使用traceback()来找到最后一个错误发生的位置.通常，它将指向您在函数中进行的调用.然后我通常将browser()放在那一点，再次运行该函数，看看出了什么问题.

You can use traceback() to locate where the last error occurred. Usually it will point you to a call you make in your function. Then I typically put browser() at that point, run the function again and see what is going wrong.

例如，这里有两个功能:

For example, here are two functions:

f2 <- function(x)
{
  if (x==1) "foo"
}

f <- function(x)
{
  f2(x)
}

请注意，f2()假定长度为1.我们可以滥用f:

Note that f2() assumes an argument of length 1. We can misuse f:

> f(NULL)
Error in if (x == 1) "foo" : argument is of length zero

现在，我们可以使用traceback()找出问题所在:

Now we can use traceback() to locate what went wrong:

> traceback()
2: f2(x) at #3
1: f(NULL)

数字表示我们在嵌套函数中的深度.因此，我们看到f调用f2并在3行给出了错误.很清楚现在，我们可以重新分配f并将browser放置在f2调用之前，以检查其输入. browser()只是允许您停止执行功能并在其环境中环顾四周.与debug和debugonce相似，不同之处在于您不必执行每一行，直到知道问题出了点为止.

The number means how deep we are in the nested functions. So we see that f calls f2 and that gives an error at line 3. Pretty clear. We could reassign f with browser placed just before the f2 call now to check it's input. browser() simply allows you to stop executing a function and look around in its environment. Similar to debug and debugonce except that you don't have to execute every line up until the point you know something goes wrong.

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