common_function::aggr

Module hll

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Two UDAFs are implemented for HyperLogLog:

  • hll: Accepts a string column and aggregates the values into a HyperLogLog state.
  • hll_merge: Accepts a binary column of states generated by hll and merges them into a single state.

The states can be then used to estimate the cardinality of the values in the column by hll_count UDF.

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