Azure Data Explorer Kusto Sort Order make_set guaranteed order of input

Question

Azure Data Explorer Kusto Sort Order make_set guaranteed order of input

databricksuser-5173 20

Hi,

https://learn.microsoft.com/en-us/kusto/query/make-set-aggregation-function?view=microsoft-fabric

Above link says "The array's sort order is undefined". Is there a way to construct the array guaranteeing preserving the order of input elements received in the input object on which make_set is applied?

Smaran Thoomu 28,225 Reputation points Microsoft External Staff Moderator

2025-08-01T12:52:34.7333333+00:00

databricksuser-5173 We haven’t heard from you on the last response and was just checking back to see if you have a resolution yet. In case if you have any resolution please do share that same with the community as it can be helpful to others. Otherwise, will respond with more details and we will try to help.

1 answer

Your answer

Smaran Thoomu 28,225 Reputation points Microsoft External Staff Moderator

2025-08-01T12:52:34.7333333+00:00

databricksuser-5173 We haven’t heard from you on the last response and was just checking back to see if you have a resolution yet. In case if you have any resolution please do share that same with the community as it can be helpful to others. Otherwise, will respond with more details and we will try to help.

Answer 1

Venkat Reddy Navari 5,255 Microsoft External Staff Moderator

Hi databricksuser-5173 You're right, make_set() does not guarantee any specific order of elements, as stated in the documentation. If preserving the input order is important, you can use make_list() instead, which does retain input order:


| summarize ordered_vals = make_list(columnName) by groupColumn

To ensure correct ordering in distributed contexts, you can add serialize before the aggregation:



| serialize
| summarize ordered_vals = make_list(columnName) by groupColumn

Note: make_list() does not remove duplicates.

I hope this information helps. Please do let us know if you have any further queries.

Kindly consider upvoting the comment if the information provided is helpful. This can assist other community members in resolving similar issues.

databricksuser-5173 20 Reputation points

2025-08-01T13:29:09.3366667+00:00

Thanks for the reply. If make_list() does not remove duplicates, can the result of make_list be deduplicated through any operator, say arg_max()? If so, will the final result be solving the very first requirement of preserving the input order received?
Venkat Reddy Navari 5,255 Reputation points Microsoft External Staff Moderator

2025-08-01T16:38:49.75+00:00
databricksuser-5173 You're correct that make_list() preserves the input order (especially when used with serialize) but does not remove duplicates. To deduplicate while preserving order, unfortunately there is no direct built-in Kusto operator that does both in one step like make_set() would, but with order preserved.

However, here's a common pattern you can use to achieve deduplication while maintaining the input order:

datatable(id:int, val:string) [ 1, "apple", 2, "banana", 3, "apple", 4, "orange" ] serialize extend row_index = row_number() summarize first_seen_index = min(row_index) by val top-hitters = top-hitters by first_seen_index asc

Or, more generally:

serialize extend row_index = row_number() summarize min_index = min(row_index) by columnName top-hitters = top-hitters by min_index asc project columnName

This approach:

Adds a row index to track input order.

Groups by the value to deduplicate.

Keeps the first occurrence based on the original order.

If you're trying to create an array (similar to make_set) with unique values in input order, you can do:

serialize extend row_index = row_number() summarize min_index = min(row_index) by columnName sort by min_index summarize ordered_unique_vals = make_list(columnName)

This will give you a list of distinct values in the order they first appeared in the input.

More info: https://learn.microsoft.com/en-us/kusto/query/?view=azure-data-explorer&preserve-view=true

Hope this helps. If this answers your query, do click Accept Answer and Yes for was this answer helpful. And, if you have any further query do let us know.

Share via

Azure Data Explorer Kusto Sort Order make_set guaranteed order of input

1 answer

Your answer