How to get number of real levels of InteractionTerm from fitted model (GLM) via StatsModels?

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Hi! This function is not based on StatsModels, but return real number of levels for InteractionTerm:

using StatsModels
function levelnum(mf, n)
    term = mf.f.rhs.terms[n]
    isa(term, InteractionTerm) || error("This term is not InteractionTerm")
    names = Tuple(t.sym for t in term.terms)
    cols = mf.data[names]
    length(unique(zip(cols...)))
end
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