hyperloglog sketches

[spinkney]

Is it possible to cache sketches of sets which you then want to do count distinct computations of? For example, I want users to be able to compose any number of groups which have each individually been passed through a hyperloglog fit. It's the same hyperloglog storage but each set is stored as a "sketch". Then I can get count distinct of each sketch or I can sum any combination of sketches to get the estimated count distinct of the union of those sketches.

This is relevant for audience estimation in digital and television advertising. See this google paper https://storage.googleapis.com/pub-tools-public-publication-data/pdf/54a28925b11e05b1d8d1cc5c03f171666dc77e8e.pdf.

[spinkney]

I believe the merge function will work which I didn't see in the documentation (let me know if I happened to miss it). Found by looking at the source code.

[joshday]

merge! is one of the core pieces of OnlineStats. It's covered in the first page of the docs.