[Rd] Extract/format/show for S4 objects

[Jeffrey J. Hallman]

The tis package has the ti (TimeIndex) class that does what you want,
and I modestly think it's nicer than the zoo stuff.

As for S4 classes, there's a good reason many of us don't use them:
they're too inflexible and hard to program with.  I wouldn't go there
unless I really had to.


Johann Hibschman <jhibschman at gmail.com> writes:

> Hi all,
>
> I'm trying to make an integer-backed quarter (as in fraction of year)
> class, but I can't quite it to work.  I want integer-backed so I don't
> have to worry about floating-point effects when doing math, and so that
> I can use it as in data.table.
>
> First of all, is there a good reference for this anywhere?  All of the
> S4 tutorials that I've found have been too high-level, and I can't find
> any examples of implementing extract.  In S3, I can use [.Date as my
> example, but I can't find the equivalent for S4.
>
> Second, is this misguided?
>
> Now for the details.  Given this start:
>
>   library(zoo) # borrowing yearqtr for output.
>   setClass("iqtr", contains="integer")
>   ## Create an iqtr object from a numeric date (e.g. 2000.5).
>   iqtr <- function (x) {
>     iq <- as.integer(floor((as.numeric(x) - 2000) * 4 + 0.0001))
>     new("iqtr", iq)
>   }
>   setMethod("show", "iqtr4",
>             function (object) {
>               cat(format(yearqtr(as.numeric(x) * 0.25 + 2000)))
>             })
>
>
> I have two issues:
>
>   1. Vectors of iqtrs do not display properly.
>      They print, but they don't look like vectors.
>        > iq <- iqtr(seq(2000, 2002, 0.25))
>        > iq
>        2000 Q2 2000 Q2 2000 Q3 2000 Q4 2001 Q2 2002 Q1> 
>
>   2. Subsets do not stay in the class.
>        > iq[1:2]
>        > [1] 0 1
>
> Clearly, I'm just not understanding what's going on.  Is there a guide
> for how to make printing, format, subsetting, etc., all work for S4
> classes?
>
> Thanks,
> Johann
>

-- 
Jeff