Custom legend labels when using group by

Hi,

I’m trying to plot a CSV file and using multiple transforms. Headers in CSV file are:

//isp_name,down_speed,up_speed,price,date

I’m using transforms as follows:

                {
                    type:'groupby',
                    groups:isp_name
                },
                {
                    type:'groupby',
                    groups:down_speed
                },
                {
                    type:'groupby',
                    groups:up_speed
                }

The issue is, while values stay the same, labels in legend are dictated by last group. Can I customize it so a combined label is shown?