[R] Superimposing y-variables in Lattice formulas
macrakis at alum.mit.edu
Sat Nov 15 18:34:28 CET 2008
On Fri, Nov 14, 2008 at 6:55 PM, Deepayan Sarkar
<deepayan.sarkar at gmail.com> wrote:
>> ...But how do I specify that I want to display all the Subjects on a... single graph, superimposing them all?
> Have you tried
> xyplot ( conc ~ time , Indometh, groups = Subject ) ?
Thanks very much for your help! That works beautifully.
Any particular reason this can't be specified in the formula? For a
small number of levels, you can write
xyplot( ifelse(Subject==1,conc,NA) + ifelse(Subject==2,conc,NA) ~ time, ...)
but obviously that doesn't generalize. I'd have thought that
something like conc*Subject or (conc | Subject) should mean the same
thing, but these aren't allowed for some reason. But I don't know what
the semantics of the formula operators are. Neither the 'formula' nor
the 'logic' man page even defines `|`, and the 'xyplot' man page only
gives examples, not a definition of the general case: "the formula is
generally of the form... can also be supplied as ... a special case is
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