[R] order of panels in xyplots

[Peter Ehlers]

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 <ehlers at 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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> 
>