Bug in StatsModels.modelmatrix()

Specific Domains Data
2

I’m closer to the problem. The term a & a and b & b got the type InteractionTerm{ContinuousTerm{Float64}}, that cannot be handled properly, instead of InteractionTerm{Tuple{ContinuousTerm{Float64}, ContinuousTerm{Float64}}}:

julia> fml2
FormulaTerm
Response:
  y(unknown)
Predictors:
  1
  a(unknown)
  b(unknown)
  a(unknown) & a(unknown)
  a(unknown) & b(unknown)
  b(unknown) & b(unknown)

julia> typeof(sfml2.rhs.terms[1])
InterceptTerm{true}

julia> typeof(sfml2.rhs.terms[2])
ContinuousTerm{Float64}

julia> typeof(sfml2.rhs.terms[3])
ContinuousTerm{Float64}

julia> typeof(sfml2.rhs.terms[4])
InteractionTerm{ContinuousTerm{Float64}}

julia> typeof(sfml2.rhs.terms[5])
InteractionTerm{Tuple{ContinuousTerm{Float64}, ContinuousTerm{Float64}}}

julia> typeof(sfml2.rhs.terms[6])
InteractionTerm{ContinuousTerm{Float64}}

so, for the time being we need to explicitly create the square terms like:

fml3 = @formula(y ~ 1 + a + (a ^ 2) + (a & b) + b + (b ^ 2));

julia> modelmatrix(fml3, df)
3×6 Matrix{Float64}:
 1.0  1.0  1.0  2.0   4.0   2.0
 1.0  2.0  4.0  3.0   9.0   6.0
 1.0  3.0  9.0  4.0  16.0  12.0

in order the avoid the problem.