如何找到发生R错误的地方？ [英] How to find where an R error occurred?

问题描述

有时候R会抛出错误，如

Sometimes R throws me errors such as

if（ncol（x）！= 2）{当我没有写这样的代码时，没有其他信息，零

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

有没有一个通用的方式来查找哪个函数导致错误？

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被压缩，所以grep不是很简单 / usr / lib / R / library 。

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

推荐答案

可以使用 traceback（）来定位最后一个错误发生的位置。通常它会指向你在你的功能中的一个电话。那么我通常会把 browser（）再次运行，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 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（）来找出出了什么问题：

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有多深。因此，我们看到 f 调用 f2 ，并且在 3 。很清楚我们可以在 f2之前放置与浏览器现在打电话来检查它的输入。 browser（）只需允许您停止执行一个功能并在其环境中环顾四周。类似于 debug 和 debugonce ，除了你不必执行每一行，直到你知道某事

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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