如何覆盖包命名空间中的不可见函数? [英] How do I override a non-visible function in the package namespace?

问题描述

我基本上想改变一个包的不可见功能.对于可见函数，即在调用 methods 时没有星号的函数，我找到了两篇如何实现目标的帖子:

I basically want to change a non-visible function of a package. For visible functions, i.e. functions that have no asterix when methods is called on them, I found two posts how I could achieve my goal:

1. 使用 assignInNamespace:参见 R-help.
2. 使用 fix:请参阅 stackoverflow

1. Use assignInNamespace: see post on R-help.
2. Use fix: see post on stackoverflow

虽然这两种方法都适用于导出/可见函数(我使用 predict.lm 作为下面第二种方法的示例，并使用 subset.data 函数测试了第一种方法.frame)，它们不适用于不可见的函数，例如预测.ar.这是为什么?有解决方法吗?

Although both approaches work for an exported / visible function (I use predict.lm as an example further below for the second approach and tested the first approach with the function subset.data.frame), they do not work for a non-visible function, e.g. predict.ar. Why is that? Is there a workaround?

这是一个最小的例子:

表明 predict.lm 可见，predict.ar 不可见:

Show that predict.lm is visible, predict.ar is not:

methods(predict)
 [1] predict.Arima*             predict.HoltWinters*       predict.StructTS*         
 [4] predict.ar*                predict.arima0*            predict.glm               
 [7] predict.lm                 predict.loess*             predict.mlm               
[10] predict.nls*               predict.poly               predict.ppr*              
[13] predict.prcomp*            predict.princomp*          predict.smooth.spline*    
[16] predict.smooth.spline.fit*

应用predict.lm:

x <- rnorm(5)
y <- x + rnorm(5)
predict(lm(y ~ x))
#          1          2          3          4          5 
#  1.0783047  1.5288031  0.3268405  0.8373520 -0.9833746

通过输入 cat("First line changed for predict.lm ") 来更改 predict.lm在函数体的开头.(您必须在编辑器中手动执行此操作):

Change predict.lm by entering cat("First line changed for predict.lm ") at the beginning of the function body. (You have to do that manually in the editor):

fix(predict.lm)
predict(lm(y ~ x))
# First line changed for predict.lm
#          1          2          3          4          5 
#  1.0783047  1.5288031  0.3268405  0.8373520 -0.983374

应用predict.ar:

sunspot.ar <- ar(sunspot.year)
predict(sunspot.ar, n.ahead=25)
# $pred
# Time Series:
# Start = 1989 
# End = 2013 

尝试改变predict.ar:

fix(predict.ar) #Here, an empty function body appears for me
fix("stats:::predict.ar") #Here as well
fix(stats:::predict.ar)
#Error in fix(stats:::predict.ar) : 'fix' requires a name

尝试使用 assignInNamespace 代替.(请注意，我只是在编辑器中复制了函数 stats::predict.ar 并添加了行 cat("First line changed for predict.ar ")在正文的开头.因为函数体很长，我这里只展示前几行)

Try to use assignInNamespace instead. (Note that I just copied the function stats:::predict.ar in an editor and added the line cat("First line changed for predict.ar ") at the beginning of the body. Because the function body is quite long, I only show the first couple of lines here)

mypredict <- function (object, newdata, n.ahead = 1, se.fit = TRUE, ...) 
{
    cat("First line changed for predict.ar
")
    if (n.ahead < 1) 
        stop("'n.ahead' must be at least 1")
    #Rest of body of stats:::predict.ar
}
assignInNamespace("predict.ar", mypredict, ns="stats")
predict(sunspot.ar, n.ahead=25)
# First line changed for predict.ar
# Error in predict.ar(sunspot.ar, n.ahead = 25) : 
#   object 'C_artoma' not found

由于First line changed for predict.ar"实际上是打印到控制台的，因此predict.ar 肯定已更改.但是，为什么找不到对象C_artoma"?

Since "First line changed for predict.ar" is actually printed to the console, predict.ar must have been changed. However, why is the object 'C_artoma' not found anymore?

更新:好的，这太尴尬了，但我不能再删除那个帖子了:答案已经在我最后提供的 Richie Cotton 回答的链接中.抱歉浪费您的时间！我想我检查了所有东西，然后我没有看到明显的东西.有人可以将此作为答案发布，我接受它.再次抱歉.

UPDATE: OK, this is super embarrassing, but I can't delete that post anymore: The answer was already at the link I provided with Richie Cotton's answer at the end. Sorry for wasting your time! I think I checked everything and then I don't see the obvious. Could someone just post this as an answer an I accept it. Sorry again.

fixInNamespace(predict.ar, pos="package:stats")

推荐答案

使用 fixInNamespace.:)

fixInNamespace("predict.ar", "stats")

或

fixInNamespace("predict.ar", pos="package:stats")

<小时>

(几年后...)
来自 Nicholas H 的评论:如果您想将某些依赖于另一个包的内部函数的代码推送到 CRAN，它将抛出构建警告并被 R-core 拒绝.如果你想要这个内部函数，你应该使用 :::: 操作符复制它并自己维护它.

---

(Several years later...)
From Nicholas H's comment: if you want to push some code to CRAN that depends upon an internal function from another package, it will throw a build warning and be rejected by R-core. If you want that internal function, you should just take a copy of it using the ::: operator and maintain it yourself.

predict.ar <- stats:::predict.ar

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