`variance`

Description

Returns the variance of a numerical expression within a group.

Variance measures how far values spread out from the mean.
Best applied when a complete dataset is available (for sampled data, use sample_variance).

Syntax

variance(expression: number): number

Arguments

Name	Type	Required	Description
expression	number	true	Numerical expression whose variance is computed

Example

Description

Use case: Compute variance of trace durations

Suppose you want to calculate how much the duration of each operation varies across traces.

Example logs

{ "operationName": "brokenPrinter", "duration": 20000 },
{ "operationName": "checkout", "duration": 250000 },
{ "operationName": "MalfunctioningDatabase", "duration": 900000 },
{ "operationName": "hipstershop.EmailService", "duration": 10000 },
{ "operationName": "checkout", "duration": 800000 },
{ "operationName": "MalfunctioningDatabase", "duration": 300000 },
{ "operationName": "brokenPrinter", "duration": 700000 },
{ "operationName": "hipstershop.EmailService", "duration": 10100 },
{ "operationName": "checkout", "duration": 1200000 },
{ "operationName": "MalfunctioningDatabase", "duration": 100000 },
{ "operationName": "brokenPrinter", "duration": 1000000 },
{ "operationName": "hipstershop.EmailService", "duration": 9950 },
{ "operationName": "MalfunctioningDatabase", "duration": 600000 },
{ "operationName": "checkout", "duration": 400000 },
{ "operationName": "brokenPrinter", "duration": 400000 },
{ "operationName": "hipstershop.EmailService", "duration": 10050 },
{ "operationName": "MalfunctioningDatabase", "duration": 500000 },
{ "operationName": "brokenPrinter", "duration": 800000 },
{ "operationName": "checkout", "duration": 600000 },
{ "operationName": "hipstershop.EmailService", "duration": 10200 }

Example query

groupby $l.operationName aggregate variance($m.duration) as duration_variance

Example output

operationName	duration_variance
checkout	58572892530.596344
MalfunctioningDatabase	67834543984.789665
brokenPrinter	110859632383.16512
hipstershop.EmailService	378315.86960154894

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