On 10 Jan, 2006, at 14:58, maechler at stat.math.ethz.ch wrote:
"Heather" == Heather Turner <Heather.Turner at warwick.ac.uk>
on Tue, 10 Jan 2006 14:30:23 +0100 (CET) writes:
Heather> This bug is not quite fixed - the example from my
Heather> original report now = works using R-2.2.1, but
Heather> plot(Uniform, 6)
Heather> does not. The bug is due
.........
g <- hatval/(1 - hatval) # Potential division by zero here
plot(g, cook, xlim = c(0, max(g)), ylim = c(0, ymx),
..........
Heather> All other values of 'which' seem to work
Heather> fine. Sorry not to have checked this in the beta
Heather> version,
(indeed; that would have been useful)
Hmm, it's not clear what *should* be drawn in such a
case. Leaving away all the observations with h_ii = 1
seems a particularly bad idea, since these are the ones that
you'd definitely should remark.
OTOH, for h_ii = 1, the cook distance is 'NaN'
(or should that be changed; to "very large" instead ???)
and plot number 6 doesn't seem to make any sense to me
When 'which = 6' was proposed
[ on R-devel as well, last April,
http://tolstoy.newcastle.edu.au/R/devel/05/04/0595.html
ah, I see, by David Firth, from your place, so, Heather, can you
make sure he sees this e-mail ?
]
I actually had wondered a bit about it's general usefulness,..
Yes, I remember that there was some discussion of this last year, and my recollection is that it was mostly luke-warm at best in regard to including this plot. The "h_ii = 1" problem can of course be taken care of by leaving out such points if they can be reliably detected, but I share Martin's unease about this. We should also worry about for example h_ii = (1 - epsilon), with epsilon small, as plotting such a point would effectively make the rest of the graph useless. Maybe it would be safest to remove the which=6 option? David