Iuri:
Your code as emailed reads:
######
data(npk, package="MASS")
fit <- by(npk, npk$block, function(bydata) fitted.values(lm(yield ~ N,
data=bydata)))
fit <- unlist(fit)
interaction.plot(npk$N, npk$block, fit, xlab="N", ylab="yield") # fake factor,
numeric fac <- c(rep(1,12),rep(2,12)) # plots everything in black
interaction.plot(npk$N, npk$block, fit, xlab="N", ylab="yield",col=fac)
cbind(npk$block,fac)
# plots everything black as well
fac <- as.factor(fac)
interaction.plot(npk$N, npk$block, fit, xlab="N",
ylab="yield",col=as.numeric(fac))
#####
Close inspection shows that the definition of fac is buried in a comment on the
fifth line of the code, so it was not running.
Having disentangled that, did you inspect fac?
fac is a length 24 vector with the first 12 values equal to 1 - corresponding
to black. You are plotting only six lines .... all of which plot correctly as
black when I run the code because the first 6 values in the colour vector you
supply are all black.
If you want to plot 6 different colour lines, try, for example, col=1:6.
Hope that helps you clear things up!
S Ellison
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