You're right, Titus. I misunderstood. It looks like index.cond
has to be in 1:(number of panels being plotted for factor f).
While this can arguably be covered by the phrase "valid indexing
vector", I agree that this could be made more explicit.
-Peter Ehlers
Titus Malsburg wrote:
Peter, thanks for your response! The problem is not how indexing
works, but rather the question what is being indexed here. If I
understand the description correctly then it is wrong. In the special
and common case where all possible levels do actually occur in the
data frame it coincidentally happens to work the way it is described
but not when the data frame contains only data points for some of the
levels. Then it appears that the indexing vector has to be bound to
1:length(unique(f)) which is unequal 1:nlevels(f). (f is a factor
here.)
Titus
On Wed, Nov 25, 2009 at 10:32 PM, Peter Ehlers <ehl...@ucalgary.ca> wrote:
Titus Malsburg wrote:
The documentation of xyplot could be improved here. It says:
"If 'index.cond' is a list, it has to be as long as the number of
conditioning
variables, and the 'i'-th component has to be a valid indexing vector
for the
integer vector '1:nlevels(g_i)' (which can, among other things, repeat
some
of the levels or drop some altogether)."
It should make explicit that nlevels is the number of levels actually
used in the data and not length(levels(f)).
It does say "... _valid_ indexing vector ..." (my emphasis).
If nlevels(g) = 5, but you're only plotting 3 panels, it seems
to me that c(3,1,5) might be a valid indexing vector.
-Peter Ehlers
Cheers,
Titus
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