定义 S4 class 继承自函数

Question

我正在尝试编写一个 S4 class，专门 returns 一个与输入长度相同的数字向量。我想我很接近；我现在遇到的问题是我只能从我的 GlobalEnv.

中的函数创建新的 classes

library(S4Vectors)

setClass("TransFunc", contains = c("function"), prototype = function(x) x)

TransFunc <- function(x) {
  if (missing(x)) return(new("TransFunc"))
  new2("TransFunc", x)
}

.TransFunc.validity <- function(object) {
  msg <- NULL
  if (length(formals(object)) > 1) {
    msg <- c(msg, "TransFunc must only have one argument.")
  }
  res1 <- object(1:5)
  res2 <- object(1:6)
  if (length(res1) != 5 || length(res2) != 6) {
    msg <- c(msg, "TransFunc output length must equal input length.")
  }
  if (!class(res1) %in% c("numeric", "integer")) {
    msg <- c(msg, "TransFunc output must be numeric for numeric inputs.")
  }
  if (is.null(msg)) return(TRUE)
  msg
}

setValidity2(Class = "TransFunc", method = .TransFunc.validity)

mysqrt <- TransFunc(function(x) sqrt(x))
mysqrt <- TransFunc(sqrt) ## Errors... why??
## Error in initialize(value, ...) : 
##   'initialize' method returned an object of class “function” instead 
##   of the required class “TransFunc”

class 直接从函数继承的好处是能够将它们用作常规函数：

mysqrt(1:5)
## [1] 1.000000 1.414214 1.732051 2.000000 2.236068 
body(mysqrt) <- expression(sqrt(x)^2)
mysqrt(1:10)
##  [1]  1  2  3  4  5  6  7  8  9 10

为什么在全局环境外传递函数会出错？

Answer 1

它不适用于 sqrt，因为 sqrt 是 primitive。

我不知道有任何函数只接受一个参数并且不是原始函数。因此，我降低了你的有效性，以演示你的代码如何与预加载包中的其他函数一起工作：

 #using your class definition and counstructor
 .TransFunc.validity <- function(object) {
   msg <- NULL
   res1 <- object(1:5)
   if (!class(res1) %in% c("numeric", "integer")) {
     msg <- c(msg, "TransFunc output must be numeric for numeric     inputs.")
   }
   if (is.null(msg)) return(TRUE)
   msg
  }  

  setValidity2(Class = "TransFunc", method = .TransFunc.validity)

这是 mean

默认版本的结果

mymean <- TransFunc(mean.default)
mymean(1:5)
[1] 3

这里有一个变通方法，通过修改 initialize 为您的 class 捕获基元并将它们转换为闭包：

#I modified the class definition to use slots instead of prototype
setClass("TransFunc", contains = c("function"))

TransFunc <- function(x) {
if (missing(x)) return(new("TransFunc"))
new2("TransFunc", x)
}
 
# Keeping your validity I changed initilalize to:

 setMethod("initialize", "TransFunc",
      function(.Object, .Data = function(x) x , ...) {
          if(typeof(.Data) %in% c("builtin", "special"))
                    .Object <- callNextMethod(.Object, function(x) return(.Data(x)),...)
              
          else 
             .Object <- callNextMethod(.Object, .Data, ...)
                                              
          
          .Object                                    
                                              
      })

我得到了以下结果

mysqrt <- TransFunc(sqrt)
mysqrt(1:5)
[1] 1.000000 1.414214 1.732051 2.000000    2.236068

编辑：
在评论中@ekoam 为您的 class:

提出了一个更通用的 initilaize 版本

setMethod("initialize", "TransFunc", function(.Object, ...) 
 {maybe_transfunc <- callNextMethod();
      if (is.primitive(maybe_transfunc)) 
          .Object@.Data <- maybe_transfunc 
      else .Object <- maybe_transfunc; 
 .Object})

编辑 2：

@ekoam 给出的方法不维护新的 class。例如：

mysqrt <- TransFunc(sqrt)
mysqrt
# An object of class "TransFunc"
# function (x)  .Primitive("sqrt")
mysqrt
# function (x)  .Primitive("sqrt")

第一个提议的方法确实有效并维护了新的 class。正如评论中所讨论的，另一种方法是在构造函数期间捕获原语，而不是创建自定义初始化方法：

library(pryr)
TransFunc <- function(x) {
  if (missing(x)) return(new("TransFunc"))
  if (is.primitive(x)) {
    f <- function(y) x(y)
    # This line isn't strictly necessary, but the actual call
    # will be obscured and printed as 'x(y)' requiring something
    # like pryr::unenclose() to understand the behavior. 
    f <- make_function(formals(f), substitute_q(body(f), environment(f)))
  } else {
    f <- x
  }
  new2("TransFunc", f)
}

定义 S4 class 继承自函数

Define S4 class inheriting from function

oop

r

r-s4