week_of_year

This page explains how to use the week_of_year function in APL.

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.

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.

Splunk SPL users

In Splunk SPL, you typically use the strftime function with the %V or %U specifiers to extract the week of the year. In APL, the week_of_year function directly extracts the ISO 8601 week number from a datetime.

Splunk example

... | eval week=strftime(_time, "%V")

ANSI SQL users

In ANSI SQL, you often use EXTRACT(WEEK FROM timestamp) or DATEPART(WEEK, timestamp). These implementations may differ slightly across platforms in how they define the first week of the year. APL uses the ISO 8601 definition via week_of_year.

SQL example

SELECT EXTRACT(WEEK FROM timestamp_column) AS week FROM events;

Usage

Syntax

week_of_year(datetime)

Parameters

Name	Type	Description
datetime	datetime	The input datetime value.

Returns

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

Use case examples

Log analysis

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 Playground

Output

week	avg_req_duration_ms
1	243.8
2	251.1
3	237.4

This query extracts the ISO week number for each record and calculates the average request duration per week.