distinctapprox(T.‘a) 🡒 number, aggregator

The aggregator computes an approximation of how many distinct elements there are. Two elements a and b are considered identical if a == b. It is provided as an alternative to distinct, but with better performance. As a rule of thumb, this aggregator is intended for vectors beyond 1 million elements.

table T = with
  [| as A, as B |]
  [| 0,   "a"   |]
  [| 0,   "a"   |]
  [| 0,   "b"   |]
  [| 1,   "b"   |]
  [| 1,   "c"   |]

table G[gdim] = by T.B

where T.B != "c"
  show table "" a1b4 with
    group by gdim

The aggregator distinctapprox supports text and number data types. It returns 0 on empty groups.

Advanced remark: The approximation is based on HyperLogLog.

See also

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