opensearch-project / opensearch-project/data-prepper

Support extracting subLists from a list

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#5,529 3 comments 0 reactions 0 assignees View on GitHub

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enhancement good first issue help wanted
Dominant language
Java
Stars
374
Forks
354
Avg merge
3d 18h
Merged PRs (30d)
8

Description

Is your feature request related to a problem? Please describe.
As a user with a field in my Events that is a List, I would like to be able to turn that list into a subList

my_list: [ 0, 1, 2, 3, 4, 5, 6]

to

my_list: [ 4, 5, 6]

or

my_list: [ 0, 1, 2 ]

or

my_list: [ 2, 3, 4]

Describe the solution you'd like
I would like a new function support in Data Prepper expressions to convert to a subList

subList(<key>, <start_index, inclusive>, <end_index, exclusive>)

An end index value of -1, could signal to extract from start_index to the end of the list.

This function could then be used in the add_entries processor like this

add_entries:
  entries:
    - key: "my_list"
      value_expression: '/subList(/my_list, 0, 2)'

Describe alternatives you've considered (Optional)
Truncate processor could support this instead

- truncate:
        entries:
          - source_keys: ["my_list"]
            length: 3
            start_at: 0

Additional context
Add any other context or screenshots about the feature request here.

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by locating the Data Prepper expressions implementation and the add_entries processor entry point. Review how existing expression functions handle list indexes, then define the inclusive-start and exclusive-end behavior, including an end index of -1, and add coverage for the requested subList examples.

Written by the indexing model from the issue text.

Assessment

Tech stack
java
Domain
data-engineering
Issue type
Feature
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
35/100

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