`stddev`

Description

Returns the standard deviation of a numerical expression within a group.

Useful for measuring how much values vary around the mean.
Best applied when a complete dataset is available (for sampled data, use sample_stddev).

Syntax

stddev(expression: number): number

Arguments

Name	Type	Required	Description
expression	number	true	Numerical expression whose standard deviation is computed

Example

Use case: Calculate the standard deviation of API latency

Traces contain a duration field representing execution time. Computing its standard deviation helps you understand the variability of API performance.

Example data

{ "operationName": "MalfunctioningDatabase", "duration": 10100 },
{ "operationName": "checkout", "duration": 350000 },
{ "operationName": "brokenPrinter", "duration": 20000 },
{ "operationName": "ScheduledEvent", "duration": 1500000 },
{ "operationName": "checkout", "duration": 100000 },
{ "operationName": "MalfunctioningDatabase", "duration": 10050 },
{ "operationName": "brokenPrinter", "duration": 400000 },
{ "operationName": "ScheduledEvent", "duration": 900000 },
{ "operationName": "checkout", "duration": 600000 },
{ "operationName": "brokenPrinter", "duration": 800000 },
{ "operationName": "ScheduledEvent", "duration": 1200000 },
{ "operationName": "checkout", "duration": 500000 },
{ "operationName": "MalfunctioningDatabase", "duration": 9950 },
{ "operationName": "ScheduledEvent", "duration": 500000 },
{ "operationName": "brokenPrinter", "duration": 1000000 },
{ "operationName": "checkout", "duration": 250000 },
{ "operationName": "MalfunctioningDatabase", "duration": 10000 },
{ "operationName": "brokenPrinter", "duration": 600000 },
{ "operationName": "ScheduledEvent", "duration": 50000 },
{ "operationName": "MalfunctioningDatabase", "duration": 9800 }

Example query

groupby $m.operationName aggregate stddev($m.duration) as latency_stddev

Example output

operationName	latency_stddev
checkout	241610.80691335752
brokenPrinter	279989.950525226
ScheduledEvent	343380.2645421216
MalfunctioningDatabase	554.8304396318806

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