There is a bug in AIC.default and AIC.lm, as illustrated below.
(I've only checked this under 1.6.1, and can't easily check if it has
already been reported since the site is down.)
> lm1 <- lm(y ~ x, list(x=1:10, y=jitter(1:10)))
> lm2 <- lm(y ~ x, list(x=1:10, y=jitter(1:10)))
> AIC(lm1, lm2)
df AIC
lm1 3 -18.662493
lm2 3 -7.265906> AIC(lm1, lm2, k = 2)
Error in "row.names<-.data.frame"(*tmp*, value
as.character(match.call()[-1])) :
invalid row.names length
The offending line is
row.names(val) <- as.character(match.call()[-1])
One possible (but probably overly complicated) solution is
> AIC.default
function (object, ..., k = 2)
{
if (length(list(...))) {
dots <- as.list(substitute(list(...)))[-1] ## added
dots <- sapply(dots, function(x) deparse(x)) ## added
rnm <- c(deparse(substitute(object)), dots) ## added
object <- list(object, ...)
val <- lapply(object, logLik)
val <- as.data.frame(t(sapply(val, function(el) c(attr(el,
"df"), AIC(el, k = k)))))
names(val) <- c("df", "AIC")
row.names(val) <- rnm ## altered
val
}
else {
AIC(logLik(object), k = k)
}
}
Alec Stephenson tel +44 (0) 1524 593950
Department of Mathematics and Statistics fax +44 (0) 1524 592681
Lancaster University a.stephenson@lancaster.ac.uk
Lancaster LA1 4YF http://www.maths.lancs.ac.uk/~stephena/
