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.
Crossfilter is not under active development, maintenance or support by Square, or its original author Mike Bostock, or the current contributors (Jason Davies, Tom Carden). We still welcome genuine bug-fixes and PRs but consider the current API and feature-set (~1.3.12) essentially complete.