rrjamie/hyperloglog is a pure-Go implementation of the HyperLogLog cardinality estimation algorithm. It allows you to approximately count distinct values from a set of data in linear time and constant space.
[1] http://algo.inria.fr/flajolet/Publications/FlFuGaMe07.pdf [2] http://stefanheule.com/papers/edbt2013-hyperloglog.pdf