[R] xyplot does not find variable in data

[Jacob Wegelin]

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