R devel - Jul 2010 - S4 class extends "data.frame", getDataPart sees "list"

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"?

Thanks.

Dan Murphy

	[[alternative HTML version deleted]]

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 at .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
>
> 	[[alternative HTML version deleted]]
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>