I'm trying to draw scatter plot of the following dataframe but it misses some points. ``` ruby df = Daru::DataFrame.new({ x: [3, 3, 3], y: [1, 2, 3] }, index: [0, 2, 3]) Plot.new [df, pt: 6, ps: 1, using: '2:3'] ``` Although if I do not specify any index then it works pretty well.