Python has a very neat package called pandas which allows for quick data transformation; tables, aggregation, that sort of thing. A lot of these types of functionality can also be found in the python itertools module. The plyR package in R is also very similar.
Usually one woud use this functionality to produce a table which is later visualized with a plot.
I am personally very fond of d3, and I would like to allow the user to first indicate what type of data aggregation he wants on the dataset before it is visualized. The visualisation in question involves making a heatmap where the user gets to select the size of the bins of the heatmap beforehand (I want d3 to project this through leaflet). I want to visually select the ideal size of the bins for the heatmap.