dayofmonth
This page explains how to use the dayofmonth function in APL.
Use the dayofmonth function in APL to extract the day number of the month from a datetime value. The function returns an integer from 1 to 31 representing the day within the month.
You can use dayofmonth to analyze patterns tied to specific days of the month, such as billing cycles, payroll processing windows, or recurring scheduled events.
Use it when you want to:
- Detect traffic or error patterns that repeat on specific days of the month.
- Group events by day of month for monthly trend analysis.
- Correlate activity spikes with known monthly schedules such as billing or report generation.
Usage
Syntax
dayofmonth(datetime)Parameters
| Name | Type | Description |
|---|---|---|
| datetime | datetime | The input datetime value. |
Returns
An int from 1 to 31 representing the day number of the month.
Use case examples
Count requests by day of month to find recurring traffic patterns.
Query
['sample-http-logs']
| extend day = dayofmonth(_time)
| summarize request_count = count() by day
| sort by day ascOutput
| day | request_count |
|---|---|
| 1 | 1450 |
| 2 | 1380 |
| 3 | 1520 |
This query groups HTTP requests by the day of the month, helping you identify days with consistently higher or lower traffic.
Find average span duration by day of month for each service.
Query
['otel-demo-traces']
| extend day = dayofmonth(_time)
| summarize avg_duration = avg(duration) by day, ['service.name']
| sort by day ascOutput
| day | ['service.name'] | avg_duration |
|---|---|---|
| 1 | frontend | 00:00:01.1200000 |
| 1 | cart | 00:00:00.4500000 |
| 2 | frontend | 00:00:01.2500000 |
This query shows how average span duration varies by day of the month for each service, useful for detecting performance changes tied to monthly cycles.
Identify which days of the month have the most failed requests.
Query
['sample-http-logs']
| where toint(status) >= 400
| extend day = dayofmonth(_time)
| summarize error_count = count() by day
| sort by error_count descOutput
| day | error_count |
|---|---|
| 15 | 98 |
| 1 | 87 |
| 28 | 76 |
This query ranks days of the month by error frequency, helping you correlate failures with recurring monthly events such as billing runs or batch jobs.
List of related functions
- dayofweek: Returns the day of the week as a timespan. Use for weekly pattern analysis rather than monthly.
- dayofyear: Returns the day of the year as an integer. Use when you need to track position within the full year.
- datetime_part: Extracts a specific date part as an integer. Use when you need flexibility to extract different parts dynamically.
- monthofyear: Returns the month number from a datetime. Use alongside
dayofmonthfor month-and-day breakdowns. - getmonth: Returns the month from a datetime as an integer.