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
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