[R] ANCOVA with many levels of one factor

[suzzy]

I am trying to do and ANCOVA with ten sites that I want to compare condition
at, with Length as a covariate. 
Most examples I have found only deal with two levels and I am unsure if the
same code applies for more than two levels. Here is what I have, and I just
wanted to double check that I am on the right track....


ancova<-lm(Condition~site+Length+site:Length)
summary(ancova)
anova(ancova)
ancova1<-update(ancova,~.-site:Length)
anova(ancova,ancova1)
summary(ancova1)

Any help/suggestions welcome! 
Thanks!

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