Well this is a bit late, but here's how you do it... Flot does not support this out of the box, but there's a perfectly good patch and plugin that will get it doing what you want.
You get them from Flot Issue #159. You'll need to patch your flot (depending on what revision you're using, there's a few copies in the issue). I had a reject or two from the patch due to using a newer revision... Then add the multi plugin to your javascript sources after flot. Finally, use multiplebars:true
in your actual plot
call's options.
Here's the general idea of what it will look like once you have the right scripts ready to go:
$.plot($("#placeholder"), [ d1, d2, d3 ], {
series: {
bars: { show: true, barWidth: 0.3, align:'center' }
},
multiplebars:true
});
You can see it in action here: http://jsfiddle.net/ryleyb/B3uGP/2/