Hi
I am having difficulty with setMethod(). I have a "brob" class of
objects whose
representation has two slots: "x" and "positive". Slot "x" (double)
holds the log
of a number and slot "positive" (logical) its sign. The idea is
that large numbers
can be handled.
I'm trying to implement a log() method using an analogue of the
setMethod() example
for polynomials on page 117 of V&R. abs() works [I think], but log()
doesn't:
[transcript follows, source for the classes below]
> a <- as.brob((-4:4 )+0.4)
> a
An object of class "brob"
Slot "x":
[1] 1.2809338 0.9555114 0.4700036 -0.5108256 -0.9162907
0.3364722 0.8754687
[8] 1.2237754 1.4816045
Slot "positive":
[1] FALSE FALSE FALSE FALSE TRUE TRUE TRUE TRUE TRUE
> abs(a)
An object of class "brob"
Slot "x":
[1] 1.2809338 0.9555114 0.4700036 -0.5108256 -0.9162907
0.3364722 0.8754687
[8] 1.2237754 1.4816045
Slot "positive":
[1] TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE
# This works: each element is now positive.
> log(a)
Error in log(x) : Non-numeric argument to mathematical function
>
What's wrong with my setMethod() call below?
setClass("brob",
representation = representation
(x="numeric",positive="logical"),
prototype = list(x=numeric(),positive=logical())
)
setAs("brob", "numeric", function(from){
out <- exp([EMAIL PROTECTED])
[EMAIL PROTECTED] <- [EMAIL PROTECTED]
return(out)
}
)
setMethod("as.numeric",signature(x="brob"),function(x){as(x,"numeric")})
is.brob <- function(x){is(x,"brob")}
"brob" <- function(x,positive){
if(missing(positive)){
positive <- rep(TRUE,length(x))
}
if(length(positive)==1){
positive <- rep(positive,length(x))
}
new("brob",x=x,positive=positive)
}
as.brob <- function(x){
brob(log(abs(x)),x>0)
}
setMethod("Math", "brob",
function(x){
switch(.Generic,
abs = brob([EMAIL PROTECTED]),
log = { out <- [EMAIL PROTECTED]
[EMAIL PROTECTED] <- NaN
out
},
acos =,
acosh =,
asin =,
asinh =,
atan =,
atanh =,
ceiling=,
cos =,
cosh =,
cumsum =,
exp =,
floor =,
gamma =,
lgamma =,
sin =,
sinh =,
tan =,
tanh =,
trunc = as.brob(callGeneric(as.numeric(x))),
stop(paste(.Generic, "not allowed on
Brobdingnagian numbers"))
)
}
)
--
Robin Hankin
Uncertainty Analyst
National Oceanography Centre, Southampton
European Way, Southampton SO14 3ZH, UK
tel 023-8059-7743
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