hll_merge() (aggregation function)

Learn how to use the hll_merge() function to merge HLL results into a single HLL value.

Merges HLL results across the group into a single HLL value.

For more information, see the underlying algorithm (HyperLogLog) and estimation accuracy.

Syntax

hll_merge (hll)

Parameters

NameTypeRequiredDescription
hllstring✔️The column name containing HLL values to merge.

Returns

The function returns the merged HLL values of hll across the group.

Example

The following example shows HLL results across a group merged into a single HLL value.

StormEvents
| summarize hllRes = hll(DamageProperty) by bin(StartTime,10m)
| summarize hllMerged = hll_merge(hllRes)

Output

The results show only the first five results in the array.

hllMerged
[[1024,14],["-6903255281122589438","-7413697181929588220","-2396604341988936699",“5824198135224880646”,"-6257421034880415225", …],[]]

Estimation accuracy

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