This example is taken from Vega's gallery

The following is the Ruby code that generates arc.json.

require 'plotrb'

data = pdata.name('table').values([12,23,47,6,52,19]).transform(pie_transform)

scale = sqrt_scale.name('r').from(data).to([20,100])

mark = arc_mark.from(data) do
    enter do
        x_start { group(:width).times(0.5) }
        y_start { group(:height).times(0.5) }
        start_angle { from :start_angle }
        end_angle { from :end_angle }
        inner_radius 20
        outer_radius { scale(scale) }
        stroke '#fff'
    end
    update do
        fill '#ccc'
    end
    hover do
        fill 'pink'
    end
end

vis = visualization.name('arc').width(600).height(400) do
    data data
    scales scale
    marks mark
end

puts vis.generate_spec(:pretty)