使用 data() 作为通用 S4 函数

发布于 2024-11-18 05:15:40 字数 1085 浏览 3 评论 0原文

我正在尝试为 foo 类定义一个新的 data 方法。我的 foo 对象遵循以下结构：

setClass(Class = "foo", 
    representation = representation(
        data = "data.frame", 
        id = "character",   
        wl = "numeric"
    )
)

我尝试创建的 data 方法实际上是访问 @data 槽的内容：

setMethod("data", "foo",
    function(object)
        object@data
)

I一直在查看第 7.1 节手册，但它只涉及 S3 类。我还浏览了这篇文章，但没有成功：

setGeneric("data", function(object, ...) standardGeneric('data'))

setMethod("data", "ANY", utils::data)

setMethod("data", "foo",
  function(object)
    object@data
)

加载包时：

> data(mtcars)
Error in function (classes, fdef, mtable)  : 
  unable to find an inherited method for function "data", for signature "data.frame"

原文

I'm trying to define a new data method for a foo class. My foo objects follow the following structure:

setClass(Class = "foo", 
    representation = representation(
        data = "data.frame", 
        id = "character",   
        wl = "numeric"
    )
)

The data method I'm trying to create is actually accessing the contents of the @data slot:

setMethod("data", "foo",
    function(object)
        object@data
)

I've been looking at the section 7.1 of the Writing R Extensions manual, but it only deals with S3 classes. I also had a peek at this post, but without success:

setGeneric("data", function(object, ...) standardGeneric('data'))

setMethod("data", "ANY", utils::data)

setMethod("data", "foo",
  function(object)
    object@data
)

When loading the package:

> data(mtcars)
Error in function (classes, fdef, mtable)  : 
  unable to find an inherited method for function "data", for signature "data.frame"

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雾里花 2024-11-25 05:15:40

Pierre，

data 的第一个参数是 ... （不是 object！），因此您需要在调度时进行一些特殊考虑。 <代码>？ dotMethods 对此进行了讨论。

通常（例如cbind、rbind），一个快速的&肮脏的解决方案是对这些函数使用 S3 方法表示法

data.foo <- function (...) {
   x <- list (...) [[1]]
   x@data
}

但是，我猜你在这里遇到了麻烦，因为原始数据函数使用了未评估的参数名称，并且错误消息表明它已被评估（确实有道理：R 如何能在调用原始数据函数之前知道参数属于哪个类（如果不求值的话？）。

所以最终使用 data() 以外的其他名称来访问数据槽可能会容易得多。

（你的 wl 插槽让我想到了波长：如果你正在为光谱数据设置一个类，请查看 hyperSpec - 它可能已经提供了您所需要的）。

Pierre,

The first argument of data is ... (not object!), so you need some special considerations for the dispatch. ? dotsMethods discusses that.

Often (e.g. cbind, rbind), a quick & dirty solution is to use S3 method notation for these functions

data.foo <- function (...) {
   x <- list (...) [[1]]
   x@data
}

However, I guess you are in trouble here because the original data function uses the unevaluated name of the argument, and the error message suggests that it is evaluated (does make sense: how could R know which class the argument has if it doesn't evaluate?) before the original data function is called.

So in the end it may be much easier to use some other name than data () to access your data slot.

(Your wl slot makes me think of wavelengths: if you are setting up a class for spectroscopic data, have a look at hyperSpec - it may provide already what you need).

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甜味超标? 2024-11-25 05:15:40

对我（我在 S3 世界中）有帮助的是创建从基本 utils 包中调用 data() 的默认函数：

data.default <- function(...){
 utils::data(...)
}

然后调度行为如预期：

data(mtcars)
mtcars
                     mpg cyl  disp  hp drat    wt  qsec vs am gear carb
Mazda RX4           21.0   6 160.0 110 3.90 2.620 16.46  0  1    4    4
Mazda RX4 Wag       21.0   6 160.0 110 3.90 2.875 17.02  0  1    4    4
Datsun 710          22.8   4 108.0  93 3.85 2.320 18.61  1  1    4    1

What helped me (I am in the S3 world) was to create default function that calls data() from the basic utils package:

data.default <- function(...){
 utils::data(...)
}

Then dispatch behaves as expected:

data(mtcars)
mtcars
                     mpg cyl  disp  hp drat    wt  qsec vs am gear carb
Mazda RX4           21.0   6 160.0 110 3.90 2.620 16.46  0  1    4    4
Mazda RX4 Wag       21.0   6 160.0 110 3.90 2.875 17.02  0  1    4    4
Datsun 710          22.8   4 108.0  93 3.85 2.320 18.61  1  1    4    1

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