`sample_stddev`

Description

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

Designed for use cases where substantial values are missing, such as when data is heavily sampled.

Note

Use sample_stddev when working with incomplete datasets (e.g., sampled trace data). For full datasets, prefer stddev.

Syntax

sample_stddev(expression: number): number

Arguments

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

Example

Use case: Calculate the standard deviation of API latency in trace data

Traces contain a duration field representing execution time. Computing its sample standard deviation helps you understand the variability of API performance even when data is incomplete.

{ "operationName": "MalfunctioningDatabase", "duration": 1200 },
{ "operationName": "Scheduled Event", "duration": 32000000 },
{ "operationName": "MalfunctioningDatabase", "duration": 6400 },
{ "operationName": "brokenPrinter", "duration": 10000 },
{ "operationName": "brokenPrinter", "duration": 60000 },
{ "operationName": "ScheduledEvent", "duration": 6000000 },
{ "operationName": "OverloadTable", "duration": 250000 },
{ "operationName": "DownloadInvoiceFunction", "duration": 300000 },
{ "operationName": "MultipleServicesOverload", "duration": 250000 },
{ "operationName": "index.lambda_handler", "duration": 1000000 },
{ "operationName": "DatabaseErrors", "duration": 800 },
{ "operationName": "DatabaseErrors", "duration": 9500 },
{ "operationName": "index.lambda_handler", "duration": 4000000 },
{ "operationName": "HeavyQueries", "duration": 45000 },
{ "operationName": "HeavyQueries", "duration": 120000 },
{ "operationName": "MultipleServicesOverload", "duration": 12000 },
{ "operationName": "DownloadInvoiceFunction", "duration": 90000 },
{ "operationName": "MalfunctioningDatabase", "duration": 8900 },
{ "operationName": "OverloadTable", "duration": 600000 },
{ "operationName": "brokenPrinter", "duration": 120000 }

groupby $l.operationName aggregate sample_stddev($m.duration)

Output

OperationName	latency_stddev
MalfunctioningDatabase	4361.089419616654
brokenPrinter	47592.67857298488
Scheduled Event	22761288.829728547
MultipleServicesOverload	83147.67135079544
index.lambda_handler	1638633.7355793486
DatabaseErrors	4238.272307063378
HeavyQueries	59570.23229162531
DownloadInvoiceFunction	152958.53824168033
OverloadTable	139481.44082183167

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