Filter and Convert Custom Dimension Values

Once a custom dimension is extracted, you can filter and analyze it like any normal column.

Filter by Text Value

requests
| where tostring(customDimensions["Region"]) == "EU"

This keeps only rows where the Region custom dimension matches the value.

Filter by Numeric Value

If the value represents a number, convert it first:

requests
| extend DurationMs = todouble(customDimensions["DurationMs"])
| where DurationMs > 1000

Reuse Extracted Values

Using extend lets you reuse the value multiple times:

traces
| extend UserId = tostring(customDimensions["UserId"])
| where UserId != ""
| summarize Count = count() by UserId

Tips

• Use extend when the value appears more than once in your query.
• Always convert to the correct type before filtering.
• Avoid comparing raw dynamic values directly.

These patterns help you build fast, readable queries that work reliably across dashboards and alerts.