`sample_variance`

Description

Returns the sample variance of a numerical expression within a group.

Useful for analyzing variability when working with incomplete datasets.
Designed for scenarios like heavy trace sampling, where global variance would be misleading.

Note

Use sample_variance when only a subset of data is available. For complete datasets, prefer variance.

Syntax

sample_variance(expression: number): number

Arguments

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

Example

Use case: Compute variance of trace durations

Suppose you want to calculate how much the duration of each operation varies across traces, even when the dataset is incomplete.

Example data

{ "operationName": "cart", "duration": 50000 },
{ "operationName": "checkout", "duration": 200000 },
{ "operationName": "brokenPrinter", "duration": 700000 },
{ "operationName": "SendOrderConfirmation", "duration": 10200 },
{ "operationName": "cart", "duration": 300000 },
{ "operationName": "brokenPrinter", "duration": 1000000 },
{ "operationName": "checkout", "duration": 900000 },
{ "operationName": "cart", "duration": 600000 },
{ "operationName": "brokenPrinter", "duration": 400000 },
{ "operationName": "SendOrderConfirmation", "duration": 9950 },
{ "operationName": "checkout", "duration": 1200000 },
{ "operationName": "cart", "duration": 100000 },
{ "operationName": "brokenPrinter", "duration": 20000 },
{ "operationName": "SendOrderConfirmation", "duration": 10050 },
{ "operationName": "checkout", "duration": 1500000 },
{ "operationName": "cart", "duration": 800000 },
{ "operationName": "brokenPrinter", "duration": 800000 },
{ "operationName": "checkout", "duration": 500000 },
{ "operationName": "SendOrderConfirmation", "duration": 10100 },
{ "operationName": "cart", "duration": 400000 }

Example query

source spans
| groupby $l.operationName aggregate sample_variance($m.duration) as duration_variance

Example output

operationName	duration_variance
brokenPrinter	56413398108.59468
cart	70558342573.80327
checkout	111286897989.06136
SendOrderConfirmation	383221.0732801104

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