I've been using var.test and bartlett.test to check basic ANOVA assumptions, among others, homoscedascity (homogeniety, equality of variances). Procedure is quite simple for One-Way ANOVA:

bartlett.test(x ~ g)  # where x is numeric, and g is a factor
var.test(x ~ g)

But, for 2x2 tables, i.e. Two-Way ANOVA's, I want to do something like this:

bartlett.test(x ~ c(g1, g2))  # or with list; see latter:
var.test(x ~ list(g1, g2))

Of course, ANOVA assumptions can be checked with graphical procedures, but what about "an arithmetic option"? Is that, at all, manageable? How do you test homoscedascity in Two-Way ANOVA?

I've been using var.test and bartlett.test to check basic ANOVA assumptions, among others, homoscedascity (homogeniety, equality of variances). Procedure is quite simple for One-Way ANOVA:

bartlett.test(x ~ g)  # where x is numeric, and g is a factor
var.test(x ~ g)

But, for 2x2 tables, i.e. Two-Way ANOVA's, I want to do something like this:

bartlett.test(x ~ c(g1, g2))  # or with list; see latter:
var.test(x ~ list(g1, g2))

Of course, ANOVA assumptions can be checked with graphical procedures, but what about "an arithmetic option"? Is that manageable? How do you test homoscedascity in Two-Way ANOVA?