Hi,
It's nice to be able to define S4 classes with slots that correspond
to standard attributes:
setClass("A1", slots=c(names="character"))
setClass("A2", slots=c(dim="integer"))
setClass("A3", slots=c(dimnames="list"))
By doing this, one gets a few methods for free:
a1 <- new("A1", names=letters[1:3])
names(a1) # "a" "b" "c"
a2 <- new("A2", dim=4:3)
nrow(a2) # 4
a3 <- new("A3", dimnames=list(NULL, letters[1:3]))
colnames(a3) # "a" "b" "c"
However, when it comes to subclassing, some of these slots cause
problems. I can extend A1:
setClass("B1", contains="A1")
but trying to extend A2 or A3 produces an error (with a non-informative
message in the 1st case and a somewhat obscure one in the 2nd):
setClass("B2", contains="A2")
# Error in attr(prototype, slotName) <- attr(pri, slotName) :
# invalid first argument
setClass("B3", contains="A3")
# Error in attr(prototype, slotName) <- attr(pri, slotName) :
# 'dimnames' applied to non-array
So it seems that the presence of a "dim" or "dimnames" slot prevents a
class from being extended. Is this expected? I couldn't find anything
in TFM about this. Sorry if I missed it.
Thanks,
H.
--
Hervé Pagès
Program in Computational Biology
Division of Public Health Sciences
Fred Hutchinson Cancer Research Center
1100 Fairview Ave. N, M1-B514
P.O. Box 19024
Seattle, WA 98109-1024
E-mail: hpa...@fredhutch.org
Phone: (206) 667-5791
Fax: (206) 667-1319
______________________________________________
R-devel@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel
