ARFF Extractor

[andrewdalpino]

Extracts ARFF files. Streaming and strict types. A nice addition. Not an Exporter though. Not that it can't be.

[Copilot]

🟡 Changes recommended

Unresolved moderate ARFF parsing and type-handling issues remain, along with documentation corrections.

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Pull request overview

Adds a streaming ARFF extractor with typed values, missing-value handling, tests, and documentation.

Changes:

• Implements ARFF parsing for numeric, integer, string, nominal, and date attributes.
• Adds fixtures and PHPUnit coverage.
• Adds documentation, navigation, and contributor guidance.

File summaries

File	Changes and final findings
tests/test.arff	ARFF test fixture. No review findings.
tests/Extractors/ARFFTest.php	Extractor test coverage. No review findings.
src/Extractors/ARFF.php	Seven moderate findings: comment handling before balance (3 votes, L170); backslash-escaped quotes (2 votes, L397); unterminated buffers at EOF (3 votes, L265); strict integer validation (3 votes, L231); preserving quoted missing markers (2 votes, L195); honoring or rejecting date formats (2 votes, L329); and double-quoted names/values (1 vote, L352).
mkdocs.yml	Adds documentation navigation. No review findings.
docs/extractors/arff.md	Two nit findings: clarify the placeholder type/description (1 vote, L8) and document the string|int union (3 votes, L17).
AGENTS.md	Updates repository guidance. No review findings.

Review details

Suppressed comments (2)

docs/extractors/arff.md:8

• The note says missing integer/date/categorical values use a placeholder string, but the constructor accepts an integer placeholder and returns it unchanged. For example, new ARFF($path, 0) produces an integer here, so describe this as the categorical placeholder rather than a string.

    Missing values, denoted by a question mark (`?`), are imported as `NAN` for numeric and real attributes and as the categorical placeholder string for integer, date, and categorical attributes. The placeholder defaults to `?`. Integer attributes are imported as PHP integers.

src/Extractors/ARFF.php:353

• Only single quotes are recognized: token(), balanced(), stripComment(), and str_getcsv() all ignore double-quoted ARFF names and values. A declaration such as @attribute "class label" string is tokenized incorrectly, so support both ARFF quote styles or explicitly reject the unsupported form.

        if (isset($string[0]) and $string[0] === "'") {
            $token = '';

• Files reviewed: 6/6 changed files
• Comments generated: 7
• Review effort level: Lite

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