Use the week_of_year function in APL to extract the ISO 8601 week number from a datetime expression. The ISO 8601 standard defines the first week of the year as the one that contains the first Thursday of the year, and weeks start on Mondays. You can use week_of_year to group records by week when analyzing trends over time. This is especially useful for weekly aggregation in dashboards, anomaly detection, and cohort analysis. Use it when you want to:
  • Track activity or metrics week by week.
  • Normalize data across different timeframes by weekly intervals.
  • Generate week-based summaries across log, trace, or security datasets.

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For users of other query languages

If you come from other query languages, this section explains how to adjust your existing queries to achieve the same results in APL.

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Usage

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Syntax

week_of_year(datetime)

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Parameters

NameTypeDescription
datetimedatetimeThe input datetime value.

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Returns

A long representing the ISO 8601 week number (from 1 to 53).

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Use case examples

Group HTTP log events by week to understand traffic trends and average request duration.Query
['sample-http-logs']
| extend week = week_of_year(_time)
| summarize avg(req_duration_ms) by week
| sort by week asc
Run in PlaygroundOutput
weekavg_req_duration_ms
1243.8
2251.1
3237.4
This query extracts the ISO week number for each record and calculates the average request duration per week.