R 使用另一个函数中的subset函数对自定义 S4 类进行子集化

我刚刚找到了this和this，它们似乎一起回答了我的问题.该问题与S4类的使用无关，而是由subset确定变量作用域的方式引起的.最初，我对subset的定义是在x@data对象中查找let.通过专门定义在x@data的范围内对表达式求值，但允许将范围扩展到parent.frame()(变量let所属的)，解决了错误，并允许我根据需要设置子集.

以下是完整的代码:

# Define class
setClass("myClass", slots = c(data = "data.frame"))

# Initiate a myClass object
dat <- new("myClass", data = data.frame(Letter = c("A", "A", "B"), Number = c(1, 2, 3)))

# Define a subset method
setMethod("subset", signature(x = "myClass"), function(x, ...) {
  condition <- substitute(...)
  indices <- eval(condition, x@data, parent.frame())
  x@data <- x@data[indices, ]
  return(x)
})

# Suppose we want to subset to only retain entries with "A"
whichletter <- "A"

# What if we have a function that should pass the subsetting value to the subset
# function?
randomFunction <- function(object, let) {
  object_subsetted <- subset(object, Letter %in% let)
  return(object_subsetted)
}

# Test it (works now)
randomFunction(object = dat, let = "A")
randomFunction(object = dat, let = "B")

An object of class "myClass"
Slot "data":
  Letter Number
1      A      1
2      A      2

An object of class "myClass"
Slot "data":
  Letter Number
3      B      3

然而，正如@jdl所强调的那样，定义一个[方法可能更明智.