[R] Lattice strip labels for two factors

[Rafael Duarte]

Dear list,
My problem is to change the strip text of lattice panels when using two 
factors.
I have a data frame with two factors:

df <- expand.grid( "fact1"=c("y","b","r"), 
"fact2"=c("far","por","lis","set"), "year"=1991:2000, "value"= NA)
df[,"value"] <- sample(1:50, 120, replace=TRUE)

I can make simple xyplot and change the text of the factor levels with 
strip.custom:

require("lattice")
xyplot( value ~ year | fact1, data=df, type="b", subset= fact2=="far",
strip = strip.custom(bg=gray.colors(1,0.95), factor.levels=c("yellow", 
"black", "red")),
layout=c(1,3)
)

But how can I change the text of the factor levels when using both 
factors as in this plot:
xyplot( value ~ year | fact1*fact2, data=df, type="b")

(fact2 levels text should change to: c("faro","porto","lisbon","setubal"))

I read the help for strip.default and the emails archive, tried with 
"which.given" but could not find out how to accomplish this.

Many thanks,
Rafael Duarte

-- 
Rafael Duarte
Marine Resources Department - DRM
IPIMAR -  National Research Institute for Agriculture and Fisheries
Av. Brasília, 1449-006 Lisbon  -  Portugal
Tel:+351 21 302 7000      Fax:+351 21 301 5948
e-mail: rduarte at ipimar.pt