[GH-2545] Add ST_Collect_Agg aggregate function

[zhangfengcdt]

Did you read the Contributor Guide?

• Yes, I have read the Contributor Rules and Contributor Development Guide

Is this PR related to a ticket?

• Yes, and the PR name follows the format [GH-XXX] my subject. Closes #<issue_number>

What changes were proposed in this PR?

• Add ST_Collect_Agg as a new spatial aggregate function

• Collects all geometries in a column into a multi-geometry (MultiPoint, MultiLineString, MultiPolygon, or
  GeometryCollection)

• Unlike ST_Union_Agg, this function does not dissolve boundaries - it simply collects geometries

• Add ST_Collect_Agg class in AggregateFunctions.scala

• Add DataFrame API support in st_aggregates.scala

• Register function in Spark SQL catalog

• Add Python API in st_aggregates.py

• Add Scala and Python tests

• Add documentation

How was this patch tested?

• Scala unit tests for various geometry types (points, polygons, mixed)
• Test GROUP BY functionality
• Test null handling (nulls are skipped)
• Test duplicate preservation (unlike ST_Union_Agg)
• DataFrame API tests (Scala and Python)

Did this PR include necessary documentation updates?

• Yes, I have updated the documentation.

[petern48]

Considering this issue (#2547), shall we maybe skip ST_Collect_Aggr and name it ST_Collect_Agg? Alternatively, we could support both if there are worries about users expecting Aggr to work. Personally think it's fine to skip _Aggr since this is a new function. @jiayuasu WDYT?

[jiayuasu]

Agree. Let's all use _agg for all new functions now. But we need to have a separate PR that allows old aggr functions to be registered under both names

[Copilot]

Pull request overview

This PR adds a new spatial aggregate function ST_Collect_Agg that collects geometries into multi-geometries without dissolving boundaries, differentiating it from the existing ST_Union_Agg function.

Key Changes:

• Implements ST_Collect_Agg aggregate function that preserves individual geometries and duplicates
• Adds DataFrame API support for both Scala and Python
• Includes comprehensive test coverage for various geometry types and edge cases

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
spark/common/src/main/scala/org/apache/spark/sql/sedona_sql/expressions/AggregateFunctions.scala	Core implementation of ST_Collect_Agg aggregator class
spark/common/src/main/scala/org/apache/spark/sql/sedona_sql/expressions/st_aggregates.scala	DataFrame API methods for ST_Collect_Agg
spark/common/src/main/scala/org/apache/sedona/sql/UDF/Catalog.scala	Registration of ST_Collect_Agg in function catalog
spark/common/src/test/scala/org/apache/sedona/sql/aggregateFunctionTestScala.scala	SQL-based tests for various use cases
spark/common/src/test/scala/org/apache/sedona/sql/dataFrameAPITestScala.scala	DataFrame API test for basic functionality
python/sedona/spark/sql/st_aggregates.py	Python API implementation with documentation
python/tests/sql/test_aggregate_functions.py	Python tests for aggregate function behavior
python/tests/sql/test_dataframe_api.py	Python DataFrame API test
docs/api/sql/AggregateFunction.md	Documentation with usage examples

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