Fast multidimensional filtering for coordinated views.
Since most interactions only involve a single dimension, and then only small adjustments are made to the filter values, incremental filtering and reducing is significantly faster than starting from scratch. Crossfilter uses sorted indexes (and a few bit-twiddling hacks) to make this possible, dramatically increasing the performance of live histograms and top-K lists. Crossfilter is available under the Apache License.
Want to learn more? See the wiki.