“S3 方法"是什么?在 R 中是什么意思? [英] What does "S3 methods" mean in R?

问题描述

由于我对 R 比较陌生，所以我不知道 S3 方法和对象是什么.我发现有 S3 和 S4 对象系统，如果可能的话，有些人建议在 S4 上使用 S3(请参阅 Google 的 R 样式指南 http://google-styleguide.googlecode.com/svn/trunk/google-r-style.html)*.但是，我不知道 S3 方法/对象的确切定义.

Since I am fairly new to R, I do not know what the S3 methods and objects are. I found that there are S3 and S4 object systems, and some recommend to use S3 over S4 if possible (See Google's R Style Guide at http://google-styleguide.googlecode.com/svn/trunk/google-r-style.html)*. However, I do not know the exact definition of S3 methods/objects.

更新:自 2019 年起，Google 的 R 风格指南超链接现位于此处.

Update: As of 2019, Google's R Style Guide hyperlink is now here.

推荐答案

大部分相关信息可以通过查看?S3或?UseMethod找到，但在简而言之:

Most of the relevant information can be found by looking at ?S3 or ?UseMethod, but in a nutshell:

S3 指的是一种方法调度方案.如果您使用过一段时间 R，您会注意到有 print、predict 和 summary 方法用于许多不同的类型对象.

S3 refers to a scheme of method dispatching. If you've used R for a while, you'll notice that there are print, predict and summary methods for a lot of different kinds of objects.

在 S3 中，这是通过以下方式工作的:

In S3, this works by:

• 设置对象的类利息(例如:a 的返回值对方法 glm 的调用具有类 glm)
• 提供一种具有一般性的方法名称(例如 print)，然后是一个点，以及然后是类名(例如:print.glm)
• 必须进行一些准备完成这个通用名称(print)为了这个工作，但如果你只是想让自己符合现有的方法名称，你不需要这个(见我提到的帮助如果你这样做，请早点).

• setting the class of objects of interest (e.g.: the return value of a call to method glm has class glm)
• providing a method with the general name (e.g. print), then a dot, and then the classname (e.g.: print.glm)
• some preparation has to have been done to this general name (print) for this to work, but if you're simply looking to conform yourself to existing method names, you don't need this (see the help I refered to earlier if you do).

对于旁观者，尤其是新创建的时髦模型拟合包的用户来说，能够输入 predict(myfit, type="class") 比 predict.mykindoffit(myfit, type="class").

To the eye of the beholder, and particularly, the user of your newly created funky model fitting package, it is much more convenient to be able to type predict(myfit, type="class") than predict.mykindoffit(myfit, type="class").

它还有很多，但这应该会让你开始.这种基于对象的属性(类)调度方法的方式有很多缺点(C 纯粹主义者可能会因为害怕它而彻夜难眠)，但在很多情况下，它工作得很好.在当前版本的 R 中，已经实现了更新的方法(S4 和参考类)，但大多数人仍然(仅)使用 S3.

There is quite a bit more to it, but this should get you started. There are quite a few disadvantages to this way of dispatching methods based upon an attribute (class) of objects (and C purists probably lie awake at night in horror of it), but for a lot of situations, it works decently. With the current version of R, newer ways have been implemented (S4 and reference classes), but most people still (only) use S3.

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