Implement WithinSubjectSplitter

[Copilot]

Implementation Plan for WithinSubjectSplitter

• Analyze existing splitter patterns and understand WithinSubjectSplitter requirements
• Design WithinSubjectSplitter class following existing patterns
• Implement WithinSubjectSplitter in moabb/evaluations/splitters.py
• Add WithinSubjectSplitter to init.py exports
• Create/update tests in test_splits.py to include WithinSubjectSplitter
• Ensure pytest parametrization compatibility
• Run tests to validate implementation (45 tests passed)
• Request code review
• Address code review feedback (fixed typo, improved docstring)
• Run security checks (0 alerts)
• Fix pre-commit formatting issues
• Update api.rst documentation
• Update whats_new.rst with Bruno Aristimunha's name

Summary

Successfully implemented WithinSubjectSplitter following the existing codebase patterns. The implementation:

Key Features:

• Performs k-fold cross-validation within each subject across all their sessions
• Compatible with pytest parametrization
• Follows the same design patterns as existing splitters
• Supports custom cv_class with StratifiedKFold as default
• Supports shuffle and random_state parameters

Files Changed:

• moabb/evaluations/splitters.py: Added WithinSubjectSplitter class (105 lines)
• moabb/evaluations/__init__.py: Exported WithinSubjectSplitter
• moabb/tests/test_splits.py: Added tests for WithinSubjectSplitter (48 lines)
• docs/source/api.rst: Added WithinSubjectSplitter to API documentation
• docs/source/whats_new.rst: Added enhancement entry with Bruno Aristimunha's name

Testing:

• All 45 tests in test_splits.py pass successfully
• Code review completed with all feedback addressed
• Security scan completed with 0 alerts
• Pre-commit checks all pass
• Documentation updated

Original prompt

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This section details on the original issue you should resolve

<issue_title>Implement WithinSubjectSplitter.</issue_title>
<issue_description>We need to follow the same style, and needs to just be compatible with the current test, i.e., pytest parametrization.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Implement WithinSubjectSplitter. #951

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[bruAristimunha]

@copilot solve the precommit

[Copilot]

Pull request overview

This PR implements WithinSubjectSplitter, a new cross-validation splitter that performs k-fold splits within each subject across all their sessions. This completes the splitter API alongside existing splitters for within-session, cross-session, and cross-subject evaluation strategies.

Changes:

• Added WithinSubjectSplitter class with stratified k-fold cross-validation across all sessions within each subject
• Exported the new splitter in the public API
• Added comprehensive test coverage with parametrized tests for compatibility and split counting

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
moabb/evaluations/splitters.py	Implemented WithinSubjectSplitter class following the same pattern as WithinSessionSplitter; fixed typo "cros-validation" → "cross-validation"
moabb/evaluations/init.py	Exported WithinSubjectSplitter in the public API
moabb/tests/test_splits.py	Added test_within_subject_compatibility, test_within_subject_get_n_splits, and extended test_custom_inner_cv parametrization; implemented eval_split_within_subject helper function

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[Copilot]

@copilot solve the precommit

Fixed in commit 84dc538. Black reformatted the test file to split the long splitter list across multiple lines. All pre-commit checks now pass.

[bruAristimunha]

You are missing the api.rst documentation, can you update?

[bruAristimunha]

@copilot, you are missing the api, the RST documentation, and the What's New " file (put my name Bruno Aristimunha). Can you update?

[Copilot]

@copilot, you are missing the api, the RST documentation, and the What's New " file (put my name Bruno Aristimunha). Can you update?

Updated in commit eebd49d. Added WithinSubjectSplitter to api.rst documentation and added enhancement entry in whats_new.rst with your name (Bruno Aristimunha).