setAs vs setIs
On Mar 16, 2008, at 8:12 PM, Christophe Genolini wrote:
Hi the list
I am fighting with the twins setAs and setIs...
Here are some questions and comments (comments to myself but that
migth
be wrong, it is why I am posting them)
1. Very surprising : using setIs define 'is', 'as<-' but not 'as' ???
2. Using setAs define 'as', 'as<-' but not 'is'...
What surprise me is that as<- can be define by both. I would have
thing
that setis is for 'is', setAs is for 'as' and 'as<-'...
Since it is not the case, is there a possibility to set with only one
function 'as', 'is' and 'as<-'
Last point, I get a warning using setAs. I did not manage to find the
name of the variable it want me to use...
### Data
setClass("B",representation(b="numeric"))
setClass("C",representation(c="numeric"))
setClass("D",representation(d="numeric"))
b <- new("B",b=3)
c <- new("C",c=4)
d <- new("D",d=5)
### using setIs
setIs("C","B",
test=function(object){return(object at c>0)},
replace=function(from,values){
from at c <- values at b^3
return(from)
}
)
is(c,"B") #Ok
as(c,"B") #not ok
It seems to me your problem here is simply that you did not define a
coerce cal in setIs, so it does not know how to turn a C object into
a B object, which is what you ask it to do here. It knows how to test
if C object is also a B object, because of the test function you
provided, and it can do the replacement you ask it in as(c,"B") <-b
because of the replace command you provided, but the third part is
missing. Perhaps something like this:
setIs("C","B",
test=function(object){return(object at c>0)},
replace=function(from,values){
from at c <- values at b^3
return(from)
},
coerce=function(from) {
new("B",b=from at c^(1/3))
}
)
as(c,"B") <- b #ok (!)
### using setAs
setAs("D","B",
function(from,to){to<-new("B",b=from at d);return(to)},
replace=function(from,values){
from at d<-values at b^2;
return(from)
}
)
is(d,"B") # not ok
as(d,"B") # ok
as(d,"B")<-b # ok
Thanks
Christophe
Haris Skiadas Department of Mathematics and Computer Science Hanover College