VegaLite plots in Julia

example_plot.jl

df = DataFrame(x=randn(500), y= randn(500))

df |> vlplot(
    mark = :point,
    encoding = (
        x = (field=:x, typ=:quantitative),
        y = (field=:y, typ=:quantitative)
    )
)

vlplot.jl

using DataFrames, CSV, JSON

function named_tuples(df::AbstractDataFrame)
    M  = Matrix(df)
    NT = NamedTuple{tuple(names(df)...), Tuple{eltypes(df)...}}
    map(1:size(M, 1)) do i
        NT(M[i,:])
    end
end
    
JSON.print(io::IO, df::AbstractDataFrame) = print(io, json(named_tuples(df)))

function vl2svg(vlspec::AbstractString)
    tmp_vlspec, tmp_svg = tempname(), tempname()
    write(tmp_vlspec, vlspec)
    run(pipeline(`vl2svg`, stdin=tmp_vlspec, stdout=tmp_svg))
    svg = read(tmp_svg, String)
    rm(tmp_vlspec); rm(tmp_svg)
    svg
end

function vlspec(spec::NamedTuple=NamedTuple{(),Tuple{}}(()); args...)
    function (df)
        with_data = (spec..., values(args)..., data=(values=JSONText(json(df)),))
        replace(json(with_data), "typ"=>"type")
    end
end

vlplot(spec::AbstractString) = display("image/svg+xml", vl2svg(spec))
vlplot(spec::NamedTuple=NamedTuple{(),Tuple{}}(()); args...) = df -> vlplot(vlspec(spec; args...)(df))