PFCOUNT

The PFCOUNT command returns the estimated cardinality (number of unique elements) observed by one or more HyperLogLog keys.

When multiple keys are provided, PFCOUNT returns the estimated cardinality of the union of the HyperLogLogs (computed by merging them internally).

Syntax

PFCOUNT key [key ...]

Parameters

• key - One or more HyperLogLog keys

Return

Integer reply: the estimated number of unique elements. If a key does not exist, it is treated as an empty HyperLogLog (count = 0).

Notes

• The result is approximate.
• With multiple keys, PFCOUNT is slower because it needs to merge registers on-the-fly.

Examples

redis> PFADD hll1 element1 element2 element3 element4 element5
(integer) 1
redis> PFADD hll2 a b c d
(integer) 1
redis> PFCOUNT hll1
(integer) 5
redis> PFCOUNT hll2
(integer) 4
redis> PFCOUNT hll1 hll2
(integer) 9