question about trailing arguments in an S4 method

 I'm trying to add arguments to the AIC method
for some classes -- things like
 weights=TRUE to calculate AIC weights
 corr=TRUE, nobs to calculate AICc
 delta=TRUE  to put a delta-AIC column in the output.

The problem is that AIC is defined as
AIC(object, ..., k=2)  where k is the constant associated
with the penalty term and ... is a list of objects
that will have their AICs calculated and listed.
Thus I'm not allowed (I think) to extend the definition to

AIC(object, ..., nobs, corr=FALSE, delta=FALSE, weights=FALSE, k=2)

 An ugly solution to this is to go through the ... list and
pull out the values of any of the other arguments I want, and
then set them to NULL, leaving the list composed only of
additional objects to calculate the AIC for.  But it seems
really ugly ...

  Any ideas for a better way to do this would be
appreciated.  (Please be gentle if possible, I'm a bit out
of my depth with S4 ...)

 cheers
   Ben Bolker

  I'm trying to add arguments to the AIC method
for some classes -- things like
  weights=TRUE to calculate AIC weights
  corr=TRUE, nobs to calculate AICc
  delta=TRUE  to put a delta-AIC column in the output.

 The problem is that AIC is defined as
AIC(object, ..., k=2)  where k is the constant associated
with the penalty term and ... is a list of objects
that will have their AICs calculated and listed.
Thus I'm not allowed (I think) to extend the definition to

AIC(object, ..., nobs, corr=FALSE, delta=FALSE, weights=FALSE, k=2)

Ben Bolker <bolker at zoo.ufl.edu> writes:

  I'm trying to add arguments to the AIC method
for some classes -- things like
  weights=TRUE to calculate AIC weights
  corr=TRUE, nobs to calculate AICc
  delta=TRUE  to put a delta-AIC column in the output.

 The problem is that AIC is defined as
AIC(object, ..., k=2)  where k is the constant associated
with the penalty term and ... is a list of objects
that will have their AICs calculated and listed.
Thus I'm not allowed (I think) to extend the definition to

AIC(object, ..., nobs, corr=FALSE, delta=FALSE, weights=FALSE, k=2)

I think you can add args before the '...'.  However, you will need to
provide values for them in all calls or else they will steal a fit
from the '...' args.

I don't understand really what you are trying to achieve, so this may
not be helpful.  Nevertheless, here is a dummy example that you may
find useful.


setClass("Foo",
         representation=representation(
           fit="lm"))

setMethod("AIC", "Foo",
          function(object, weights=TRUE, delta=TRUE, ..., k=2) {
              ans <- AIC(object=object at fit, k=k, ...)
              args1 <- list(weights=weights, delta=delta, k=k)
              cat("args\n")
              print(args1)
              cat("answer:\n")
              print(ans)
          })

example("AIC")
foo <- new("Foo", fit=lm1)
AIC(foo)
## AIC(foo, lm1)   # this doesn't work, lm1 gets picked up as the weights arg
AIC(foo, weights=FALSE, delta=TRUE, lm1, lm1, lm1)



+ seth

He wants to specify arguments to AIC that act like the "k" argument
and is thinking of faking it by, essentially, doing another round of
argument matching on ...

I think that if you define an S4 generic that only dispatches on the
first argument you may be able to do it for a specific method. On the
bright side, the new documentation for AIC would take precedence over
the stats documentation so the users couldn't actually complain about
the method not matching the documentation.