On Jun 20, 2011, at 10:49 AM, Bert Gunter wrote:
> Hi all:
>
> Thanks, David. This is a good example of knowledgeable "R forensic
> investigation." I leave it to Frank whether it meets his criteria.
>
> However, I would argue that that this is bad practice and quite
> unwise. In general, these details are implementation dependent and
> could change. Yes, they are exposed, but only because everything is in
> R. The more desirable and safer way to do things would be to use
> accessor functions. I believe Frank's question was to ask whether such
> accessor functions exist. If they do not, then of course one is stuck
> with writing one based on details like thoseyou have elucidated. But
> this is really not good programming practice, imo.
>
> Contrary and more informed views welcome.
All reasonable comments. I would offer in my defense (but of only the
second suggestion) the documentation of the lattice-object:
http://finzi.psych.upenn.edu/R/library/lattice/html/trellis.object.html
... which does suggest that one can rely on $condlevel being a
designed named component of a lattice-object.
The strip.default and strip.custom functions access a variable in the
environment of the lattice object creation named "var.name" but I do
not see of a method to access its values without using the "<<-"
construction .... generally thought to violate "good practice".
--
David
>
> Cheers,
> Bert
>
> On Mon, Jun 20, 2011 at 7:17 AM, David Winsemius <dwinsemius at comcast.net
> > wrote:
>>
>> Frank Harrell wrote:
>>>
>>> I know about the current.row, current.column, and panel.number
>>> functions
>>> that are useful within panel functions written for lattice. Are
>>> there
>>> easy ways to obtain the names of the conditioning variables (those
>>> appearing after |) and their values for the current panel?
>>> Thanks
>>> Frank
>>>
>>
>> Using one of the examples in help(xyplot):
>>
>> states <- data.frame(state.x77,
>> state.name = dimnames(state.x77)[[1]],
>> state.region = state.region)
>> testp <- xyplot(Murder ~ Population | state.region, data = states,
>> groups = state.name,
>> panel = function(x, y, subscripts, groups) {
>> ltext(x = x, y = y, labels = groups[subscripts], cex=1,
>> fontfamily = "HersheySans")
>> })
>> str(testp)
>>
>> I see that the names of the state.regions are in an attribute of
>> testp$packet.sizes, so:
>>
>>> attr(testp$packet.sizes, "dimnames")[["state.region"]][4]
>> #[1] "West"
>>
>> #Looking for a further example in help(xyplot with 2 "panel
>> dimensions" I
>> tried:
>>
>>> testp2 <- dotplot(variety ~ yield | year * site, data=barley)
>>
>> #I'm not quite sure how the "rows" and "columns" are defined , but
>> I get:
>>
>>> attr(testp2$packet.sizes, "dimnames")[[1]][2]
>> [1] "1931"
>>> attr(testp2$packet.sizes, "dimnames")[[2]][1]
>> [1] "Grand Rapids"
>>
>> I'm not sure this is the "right answer" because after looking
>> further, I now
>> see a list node entitled $condlevels which returns the same
>> information is a
>> much more straightforward fashion:
>>
>>> testp2 $ condlevels
>> $year
>> [1] "1932" "1931"
>>
>> $site
>> [1] "Grand Rapids" "Duluth" "University Farm" "Morris"
>> [5] "Crookston" "Waseca"
>>
>> (And other nodes that contain information about conditioning levels:
>> $ index.cond :List of 2
>> ..$ : int [1:2] 1 2
>> ..$ : int [1:6] 1 2 3 4 5 6
>> $ perm.cond : int [1:2] 1 2
>> $ condlevels :List of 2
>> ..$ year: chr [1:2] "1932" "1931"
>> ..$ site: chr [1:6] "Grand Rapids" "Duluth" "University Farm"
>> "Morris" ...
>>
>> HTH;
>>
>> David.
>>
>> --
>> View this message in context: http://r.789695.n4.nabble.com/Accessor-functions-in-lattice-graphics-tp3609435p3611509.html
>> Sent from the R help mailing list archive at Nabble.com.
>>
>> ______________________________________________
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>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>>
>
>
>
> --
> "Men by nature long to get on to the ultimate truths, and will often
> be impatient with elementary studies or fight shy of them. If it were
> possible to reach the ultimate truths without the elementary studies
> usually prefixed to them, these would not be preparatory studies but
> superfluous diversions."
>
> -- Maimonides (1135-1204)
>
> Bert Gunter
> Genentech Nonclinical Biostatistics
David Winsemius, MD
West Hartford, CT