Ask HN: Visualization + serious calculations, how do you do it?

I'm building visualizations that require some serious calculations - what's the best way to do so?

Here's an example. On the easy end, I've got a visualization running on top a simple k-means clustering. Clustering with any meaningful dataset kills my window.

Do people just set up backends for python or R to handle this? Or are you doing web-workers? What's the quickest setup?