How can I access custom event values from Azure AppInsights analytics? - azure

Question

I am reporting some custom events to Azure, within the custom event is a value being held under the customMeasurements object named 'totalTime'.
The event itself looks like this:
loading-time: {
customMeasurements : {
totalTime: 123
}
}
I'm trying to create a graph of the average total time of all the events reported to azure per hour. So I need to be able to collect and average the values within the events.
I can't seem to figure out how to access the customMeasurements values from within the Azure AppInsights Analytics. Here is some of the code that Azure provided.
union customEvents
| where timestamp between(datetime("2019-11-10T16:00:00.000Z")..datetime("2019-11-11T16:00:00.000Z"))
| where name == "loading-time"
| summarize Ocurrences=count() by bin(timestamp, 1h)
| order by timestamp asc
| render barchart
This code simply counts the number of reported events within the last 24 hours and displays them per hour.
I have tried to access the customMeasurements object held in the event by doing
summarize Occurrences=avg(customMeasurements["totalTime"])
But Azure doesn't like that, so I'm doing it wrong. How can I access the values I require? I can't seem to find any documentation either.

Answer 1

It can be useful to project the data from the customDimensions / customMeasurements property collecton into a new variable that you'll use for further aggregation. You'll normally need to cast the dimensions data to the expected type, using one of the todecimal, toint, tostring functions.
For example, I have some extra measurements on dependency telemetry, so I can do something like so
dependencies
| project ["ResponseCompletionTime"] = todecimal(customMeasurements.ResponseToCompletion), timestamp
| summarize avg(ResponseCompletionTime) by bin(timestamp, 1h)
Your query might look something like,
customEvents
| where timestamp between(datetime("2019-11-10T16:00:00.000Z")..datetime("2019-11-11T16:00:00.000Z"))
| where name == "loading-time"
| project ["TotalTime"] = toint(customMeasurements.totalTime), timestamp
| summarize avg(TotalTime) by bin(timestamp, 1h)
| render barchart