[FR] Cross product

[mmikhasenko]

A prototype is below. Should go to separate branch, and merged once ready

struct xProductPDF{N}
    dims::SVector{N,pdf}
    keys::SVector{N,Symbol}
end

xProductPDF(; kwargs...) = xProductPDF{length(kwargs)}(SVector(values(kwargs)...), SVector(keys(kwargs)...))

function generate(N, X::xProductPDF; kwarg...)
    data_vectors = generate.(N, X.dims; kwarg...)
    ntv = NamedTuple{Tuple(X.keys)}.(zip(data_vectors...))
    return ntv
end

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@testset "cross-product PDF" begin
    # test
    pdf1 = pdf((x;p)->x.^2; lims=(-1,2), p=∅)
    pdf2 = pdf((x;p)->x.^4; lims=(-1,2), p=∅)
    X = xProductPDF(;x=pdf1, y=pdf2)
    s = generate(100, X)
    # 
    @test length(s) == 100
    @test hasproperty(s[1], :x)
    @test hasproperty(s[1], :y)
    # 
    s = generate(50, X; Nbins=300)
    @test length(s) == 50
end