r - 如何在 R 中自动更新 S4 类的插槽

Question

我在 R 中使用 S4 对象并想知道以下问题:

让我们假设以下简化示例:我们在 R 中有两个 S4 类，一个名为 客户 和另一个 订购 .我们使用以下插槽定义它们:

Customer <- setClass(Class = "Customer",slots = c(CustomerID = "numeric", Name = "character", OrderHistory = "data.frame"),
                     prototype = list(CustomerID = 0,Name = "",OderHistory = data.frame()))

Order <- setClass(Class = "Order",slots = c(CustomerID = "numeric", Description = "character",
                                               Cost = "numeric"), 
                     prototype = list(CustomerID = 0,Description = "",Cost = 0))


# constructor

Customer <- function(CustomerID, Name, OrderHistory=data.frame()){
  #drop sanity checks
  new("Customer",CustomerID = CustomerID, Name = Name, OrderHistory = OrderHistory)
}

Order <- function(CustomerID, Description = "",Cost = 0){
  #drop sanity checks
  new("Order",CustomerID = CustomerID, Description = "", Cost = 0)
}

#create two objects

firstCustomer <- Customer(1,"test")

firstOrder <- Order(1,"new iPhone", 145)

显然，firstCustomer 和 firstOrder 是通过 CustomerID 链接的。创建新的 Order 实例后，是否可以自动更新 Customer 的 OrderHistory 槽？假设 OrderHistory 有两列，“描述”和“成本”，我如何自动更新一个新的订单实例？有没有一种优雅/通用的方法来做到这一点？最有可能的是，Order 类需要一个类型为“Customer”的槽。提前谢谢了

Answer 1

您无法链接两个独立的对象，因此您需要使用两者的方法。这是一个带有替换方法的示例:

Customer <- setClass(
  "Customer", 
  slots=c(
    CustomerID="numeric", 
    Name="character", 
    OrderHistory="list"
  ),
  prototype=list(OrderHistory = list())
)
Order <- setClass(
  Class="Order", 
  slot =c(
    Description="character", Cost="numeric"
) )

setGeneric(
  "add<-", 
  function(object, value, ...) StandardGeneric("add<-")
)
setMethod("add<-", c("Customer", "Order"), 
  function(object, value) {
    object@OrderHistory <- append(object@OrderHistory, value)
    object    
  }
)
setMethod("show", "Customer", 
  function(object) {
    cat("** Customer #", object@CustomerID, ": ", object@Name, "\n\n", sep="")
    for(i in object@OrderHistory) cat("\t", i@Description, "\t", i@Cost, "\n", sep="")
  }
)

firstCustomer <- new("Customer", CustomerID=1, Name="test")
add(firstCustomer) <- new("Order", Description="new iPhone", Cost=145)
add(firstCustomer) <- new("Order", Description="macbook", Cost=999)

firstCustomer

产生:

** Customer #1: test

  new iPhone  145
  macbook 999