[R] xyplot does not find variable in data

[Bert Gunter]

Deepayan will correct me if I'm wrong, but I'm pretty sure that the answer
is that it looks in the frame in the data argument only for variables in the
formula argument. Note that the fact that it also works for the subset
argument is explicitly mentioned therein:

subset:  logical or integer indexing vector **(can be specified in terms of
variables in data). **

FWIW, I agree that this is not as clearly documented as I think it could be:
I kind of intuited it after a bunch of trial and error.

Bert Gunter
Genentech Nonclinical Biostatistics


 
 -----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On
Behalf Of Jacob Wegelin
Sent: Monday, October 12, 2009 9:33 AM
To: r-help at stat.math.ethz.ch
Subject: [R] xyplot does not find variable in data

When we call a lattice function such as xyplot, to what extent does
the "data" designation cause the function to look inside the "data"
for variables?

In the examples below, the "subset" argument understands that
"Variety" is a variable in the data.

But the "scales" argument does not understand that "nitro" is a
variable in the data.

What principle is at work?


library(MEMSS)

# The following works fine:

xyplot(
	yield ~ nitro
	, data=Oats
	, scales=list(
		x=list(
			at=unique(Oats$nitro)
			)
		)
	, subset=Variety=="Victory"
)

# But the following returns an error:

xyplot(
	yield ~ nitro
	, data=Oats
	, scales=list(
		x=list(
			at=unique(nitro)
			)
		)
)

Thanks for any insight

Jacob A. Wegelin
Assistant Professor
Department of Biostatistics
Virginia Commonwealth University
730 East Broad Street Room 3006
P. O. Box 980032
Richmond VA 23298-0032
U.S.A.
E-mail: jwegelin at vcu.edu
URL: http://www.people.vcu.edu/~jwegelin

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