[Rd] Subsetting using dimnames on S4 array-based class

Iago Mosqueira imosqueira at suk.azti.es
Thu Feb 17 13:37:56 CET 2005


I did send this message to r-help and got no reply, no I am resubmitting
here in case this was a bit too specific for the other list.

Many thanks,


Iago Mosqueira
<imosqueira at suk.azti.es>
r-help at stat.math.ethz.ch
Subsetting using dimnames on S4
array-based class
Fri, 11 Feb 2005 08:29:03 +0000


I am encountering some problems when overloading the "[" operator for a
new S4 class based on array. This is an example class definition:

        prototype(array(NA, dim=c(3,3)), 
        dimnames=list(age=1:3, year=10:12))

And this the corresponding setMethod with print estatements to see what
is being passed:

setMethod("[", signature(x="foo"),
    function(x, i="missing", j="missing", ..., drop="missing") {
        print(paste("i:", i))
        print(paste("j:", j))

So I first create a new object and load it with some data:

> x <- new("foo")
> x[,] <- 1:9

And then apply subsetting without using the dimension names and see what
are the values of i and j inside the function:

> x[1:2,'10']
[1] "i: 1" "i: 2"
[1] "j: 10"

Both i and j hold exactly what was expected here. But if I use the
dimension names, the subsetting indices does not seem to be passed as I

> x[age=1:3, year=1:3]
[1] "i: missing"
[1] "j: missing"
> x[, year='10']
[1] "i: missing"
[1] "j: missing"

Subsetting with dimnames appears to work without trouble on an array,
which "foo" extends:

> s[1,2:3]
2 3 
4 7 
> s[age=1,year=2:3]
2 3 
4 7

Although dimnames seem to be in fact simply ignored:

> s[a=1,b=3]
[1] 7

Linux Debian 3.0
R 2.0.0

Do I need to define my class differently for subsetting using dimnames
to work? Even if they are not really being checked, I would like to be
able to use subsetting in this way as it makes code more readable when
using arrays with many dimensions.

Many thanks,

Iago Mosqueira

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