I replied off list, accidentally, below. Christophe then asked
>> Probably you want to write a method for 'length' with signature x = 'E'.
>
> Well you're right. Consider the following code :
>
> setClass("A",representation(nb="numeric",li="list"))
> setMethod(
> "show",
> "A",
> function(object){
> for(i in 1:[EMAIL PROTECTED]){print([EMAIL PROTECTED])}
> }
> )
You want to use seq_along([EMAIL PROTECTED]) rather than 1:[EMAIL PROTECTED]
(which
fails when [EMAIL PROTECTED] is 0-length)
> x <- list()
> for (i in seq_along(x)) cat(x[[i]], "\n")
>
(no error, no output). 'for (i in 1:x)'-style iterations also surprise
when x=0. Also, 'cat' is used more often in 'show' methods, perhaps
because it imposes less formating on the output and hence allows the
'show' method to have more control over compactly representing the
complex S4 objects.
> # this works
> new("A",nb=2,li=list("E","R"))
>
> # this does not
> new("A")
>
> So I want to define show with first detecting if the object A is the empty
> object or not.
>
>> Probably you want to write a method for 'length' with signature x = 'E'. >
>> slotNames and getSlots might help you to write a function that visits all
>> slots.
>
> Reading what you say (but I did non try yet), I think to define a length
> function for class "A" that will be the sum of the length of all the slot,
> then I will test length(a)!=0
>
> Christophe
[off-list reply, oops]
Christophe Genolini wrote:
> Hi the list,
>
> With basic type, length gives the length of the vector
> Wtih list, length gives the number of item
> With S4 object, length gives...one. Even with an objet with empty slot.
not quite; if the class extends a class for which there is a length
method, then, e.g.,
> setClass("E", "numeric")
[1] "E"
> length(new("E"))
[1] 0
Probably you want to write a method for 'length' with signature x = 'E'.
slotNames and getSlots might help you to write a function that visits
all slots. object.size will give you the physical size of the object,
but this is probably not what you want.
Martin
> setClass("E",representation(e="numeric"))
> [1] "E"
> length(new("E"))
> [1] 1
> setClass("E",representation(e="matrix"))
> [1] "E"
> length(new("E"))
> [1] 1
>
> Is there a way to get the real length of an S4 objet ? Furthermore,
is there a simple way to detect that an object is has all its slot to
object of size zero ?
>
> Thanks
>
> Christophe
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