On 7/11/10 9:08 PM, Daniel Murphy wrote:
R-Devel:
When I get the data part of an S4 class that contains="data.frame", it gives
me a list, even when the "data.frame" is the S4 version:
d<-data.frame(x=1:3)
isS4(d)
[1] FALSE # of course
dS4<-new("data.frame",d)
isS4(dS4)
[1] TRUE # ok
class(dS4)
[1] "data.frame" # good
attr(,"package")
[1] "methods"
setClass("A", representation(label="character"), contains="data.frame")
[1] "A"
a<-new("A",dS4, label="myFrame")
getDataPart(a)
[[1]] # oh?
[1] 1 2 3
class(a...@.data)
[1] "list" # hmm
names(a)
[1] "x" # sure, that makes sense
a
Object of class "A"
x
1 1
2 2
3 3
Slot "label":
[1] "myFrame"
Was I wrong to have expected the "data part" of 'a' to be a "data.frame"?
Yes. Also, there is a clue in the documentation for getDataPart:
"rarely suitable to be called directly"
The data part, aka "data slot", generally does not have a class (S4 or S3).
You are probably looking for S3Part():
> setClass("myFrame", contains = "data.frame")
[1] "myFrame"
> z = new("myFrame", data.frame(x=1:3))
> z
Object of class "myFrame"
x
1 1
2 2
3 3
> S3Part(z)
Object of class "data.frame"
x
1 1
2 2
3 3
> S3Part(z, strictS3 = TRUE)
x
1 1
2 2
3 3
Thanks.
Dan Murphy
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