Easy Group By

function formatTooltipAsHours(value, ratio, id, index)
{
	return value.toFixed(2) + ' h';
}

function formatTooltipAsHoursWithDays(value, ratio, id, index)
{
	var hours = parseInt(value);
	var days = parseInt(hours / 24);
	value = value - days * 24;
	if (days > 0)
	{
		return days + 'd, ' + value.toFixed(2) + ' h';
	}
	return value.toFixed(2) + ' h';
}

var c3arg = {
	onrendered: updateFrameHeight,
	data: chartData,
	axis: {
		x: {
			type: 'category', // this is needed to load string x value
			label: {
				text: chartData.custom.xLabel,
				position: 'outer-left'
			}
		},
		y: {
			label: chartData.ytype
		}
	}
};

if (chartData.custom && chartData.custom.tooltip)
{
	var tooltipFunction = eval(chartData.custom.tooltip);
	c3arg.tooltip = {
		format: {
			value: tooltipFunction
		}
	};
}

c3.generate(c3arg);