The Group by operator provides the Standard deviation aggregation in Eventstream

DP-700 By islever Editorial Last updated Sep 26, 2026

Ingest and transform streaming data

Short answer

B The Eventstream Group by operator includes Standard deviation in its aggregations, while Aggregate only offers Average, Max, Min, and Sum.

Question

You have a Fabric workspace that contains an eventstream named Eventstream1. Eventstream1 processes data from a thermal sensor by using event stream processing, and then stores the data in a lakehouse. You need to modify Eventstream1 to include the standard deviation of the temperature. Which transform operator should you include in the Eventstream1 logic?

Expand
Group by Correct Answer
Union
Aggregate

Key Takeaways

In the Eventstream event processor, Standard deviation is available only in the Group by operator, not in Aggregate - a deliberate trap between the two aggregation operators.

To add the standard deviation of the temperature in Eventstream1, use the Group by transform operator, whose aggregation list includes Standard deviation; the Aggregate operator only offers Average, Max, Min, and Sum.

Common mistake: Choosing Aggregate because standard deviation is conceptually an aggregation; in Eventstream the Aggregate operator exposes only Average, Max, Min, and Sum.

Expert Analysis

Why the Answer Is Correct

The Eventstream event processor's Group by operator includes Standard deviation in its aggregation functions, so adding a Group by transform over the temperature field produces the required standard deviation. Microsoft's event processor documentation lists Standard deviation among the Group by aggregations, while the simple Aggregate operator exposes only Average, Max, Min, and Sum.

Why the Other Options Are Wrong

Option D (Aggregate) cannot compute standard deviation because it only offers Average, Max, Min, and Sum. Option A (Expand) flattens arrays or records into separate rows or columns and performs no aggregation. Option C (Union) combines events from multiple streams and does no aggregation either.

Community Comment Notes

The community strongly favors B (93 votes). GHill1982 (7 likes) states the Group by operator contains the Standard deviation aggregation while Aggregate only has Average, Max, Min, and Sum, and 405a659 links the event processor editor documentation confirming it.

Official Reference

https://learn.microsoft.com/en-us/fabric/real-time-intelligence/event-streams/process-events-using-event-processor-editor

This link opens the official vendor documentation in a new tab.

Community Votes

100%

100% of anonymous learners picked answer B. Votes are pick records left by other test-takers — they are not the verified answer.

Discussion 5 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 5

GHill1982 👍 7 Answered B

The Group by transform operator contains the Standard deviation aggregation. The Aggregate transform operator only contains Average, Max, Min and Sum aggregation.
405a659 👍 5 Answered B

https://learn.microsoft.com/en-us/fabric/real-time-intelligence/event-streams/process-events-using-event-processor-editor?pivots=standard-capabilities#group-by
MultiCloudIronMan 👍 1 Answered D

while Group by is useful for creating groups, it does not provide the full range of aggregate functions that Aggregate does, including the standard deviation. This is why the Aggregate operator is the correct choice.
Loursticks1111 👍 1 Answered B

Standard Deviation is only available in Group by, not Aggregate operator
abdulbasit170 👍 1 Answered B

Group by is the correct answer

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