[R] S4 into a data frame

[Martin Morgan]

On 06/18/2012 01:49 PM, spf385 wrote:
> Greetings,
>
> I'm still very new to R; however I have been tasked with converting an S4
> object into a data.frame. We are just trying to learn the basics of S4.
> Could anyone offer a 'simple' example of coercing an S4 object (such as
> might be stored in a package attribute) into a data.frame? Ultimately, we
> would like to do something along the lines of
>
> mydata<- as.data.frame(original S4 object)

see ?setAs for more extensive discussion.

Not sure what 'stored in a package attribute might mean'. Here's a class

  setClass("A", representation(x="numeric", y="numeric"))

and how to coerce from "A" to a "data.frame"

  setAs("A", "data.frame", function(from) data.frame(x=from at x, y=from at y))

and then in action

 > a = new("A", x=1:5, y=5:1)
 > as(a, "data.frame")
   x y
1 1 5
2 2 4
3 3 3
4 4 2
5 5 1

To use as.data.frame(a), you'd have to implement the 'as.data.frame.A' 
S3 method, e.g.,

  as.data.frame.A = function(x) as(x, "data.frame")

Also, probably you'd want a validity method (see ?setValidity) on "A", 
to ensure that x, y were equal length.

Martin

>
> Thanks in advance!
>
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