ML command supports category_field parameter

[gaobinlong]

Description

From the document of ML command, it shows that ml supports category_field command, but actually it doesn't work. This PR makes ML command supports category_field parameter.

Request:

POST _plugins/_ppl?format=jdbc
{
  "query":"source = abcd_test | eval value = cast(value as double) | fields value, category | ml action='trainandpredict' algorithm='rcf' input='value' category_field='category'"
}

Response:

{
  "schema": [
    {
      "name": "value",
      "type": "double"
    },
    {
      "name": "category",
      "type": "string"
    },
    {
      "name": "score",
      "type": "double"
    },
    {
      "name": "anomalous",
      "type": "boolean"
    }
  ],
  "datarows": [
    [
      1,
      "a",
      0,
      false
    ],
    [
      2,
      "b",
      0,
      false
    ]
  ],
  "total": 2,
  "size": 2
}

Related Issues

#3406

Check List

• New functionality includes testing.
• New functionality has been documented.
• New functionality has javadoc added.
• New functionality has a user manual doc added.
• API changes companion pull request created.
• Commits are signed per the DCO using --signoff.
• Public documentation issue/PR created.

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[gaobinlong]

@LantaoJin @qianheng-aws @songkant-aws please help to review this PR, thanks!

[opensearch-trigger-bot]

This PR is stalled because it has been open for 30 days with no activity.

[songkant-aws]

LGTM

[songkant-aws]

@LantaoJin @qianheng-aws @yuancu Need other reviews.

[LantaoJin]

categoryField is null will throw NPE in generateCategorizedInputDataset

[Swiddis]

How so? generateCategorizedInputDataset has null checking:

sql/opensearch/src/main/java/org/opensearch/sql/opensearch/planner/physical/MLCommonsOperatorActions.java

Line 83 in 0c1ec27

ExprValue categoryValue = categoryField == null ? null : tupleValue.get(categoryField);

If we want, we can add a @Nullable annotation to that field to document that contract in the signature

[opensearch-trigger-bot]

This PR is stalled because it has been open for 2 weeks with no activity.

[opensearch-trigger-bot]

This PR is stalled because it has been open for 2 weeks with no activity.

[Swiddis]

@LantaoJin can you re-review?

[opensearch-trigger-bot]

This PR is stalled because it has been open for 2 weeks with no activity.