I would respectfully request anyone wanting to implement ANOVA to first read Bill Venables’ (of Venables and Ripley, Modern Applied Statistics with S fame) famous unpublished paper Exegeses on Linear Models.
I am probably too hard-line about always defining anova as a comparison of the fits of two nested (in the sense that one is a special case of the other) linear models but that is because I have spent so much of my life explaining why p-values from certain anova tables don’t make sense.