CODEWITHSUNDEEP
roopinheritancer-s4
Raad
Raad

Reputation: 2715

Extend data.frame class in R to inherit data.frame methods

I am having trouble defining a class that inherits all of a data.frame's methods. For example, if I was to define a class timeline this could be represented as a data.frame:

data.frame(task = c("Read Permutation City", "Learn S4 oop"), 
           from = c(Sys.Date(), Sys.Date()),
           to = c(Sys.Date() + 5, Sys.Date() + 1))

Instead I would like to define a class "timeline" that would retain all of a data.frames methods but override and add several methods (e.g. plot, summary and window). In other languages this is fairly straightforward.

I would like to do this using an S4 class structure. I tried to implement an S4 class using the contains argument, however, I must be doing something wrong as the results are not what you expect from a data.frame.

timeline <- setClass(Class = "timeline", contains = "data.frame")

timeline <- function(task, from, to) {
  new("timeline", data.frame(task = task, from = from, to = to))
}

tm <- timeline("Run", Sys.Date(), Sys.Date() + 5)
getClass("timeline") # Class "timeline" .... Extends: Class "data.frame", directly
inherits(tm, "data.frame") # TRUE

nrow(tm) # 0
ncol(tm) # 3

tm # Prints S4 info
print(tm) # Expected output

What is the right way of doing this?

Upvotes: 5

Views: 631

Answers (1)

Martin Morgan
Martin Morgan

Reputation: 46856

use setOldClass("data.frame") before setClass().

Upvotes: 1

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