Implementation of both use_clones and fit_base_estimators

[nilichen]

Description

This PR is to implement both use_clones and fit_base_estimators (previously called refit in EnsembleVoteClassifier) for EnsembleVoteClassifier and StackingClassifier. As well as added corresponding tests for these two parameters.

Will have another PR to address StackingRegressor and StackingCVRegressor.

Related issues or pull requests

Towards #627. See also #383.

Pull Request Checklist

• Added a note about the modification or contribution to the ./docs/sources/CHANGELOG.md file (if applicable)
• Added appropriate unit test functions in the ./mlxtend/*/tests directories (if applicable)
• Modify documentation in the corresponding Jupyter Notebook under mlxtend/docs/sources/ (if applicable)
• Ran PYTHONPATH='.' pytest ./mlxtend -sv and make sure that all unit tests pass (for small modifications, it might be sufficient to only run the specific test file, e.g., PYTHONPATH='.' pytest ./mlxtend/classifier/tests/test_stacking_cv_classifier.py -sv)
• Checked for style issues by running flake8 ./mlxtend

[pep8speaks]

Hello @nilichen! Thanks for updating this PR. We checked the lines you've touched for PEP 8 issues, and found:

• In the file mlxtend/classifier/ensemble_vote.py:

Line 291:80: E501 line too long (80 > 79 characters)

• In the file mlxtend/classifier/stacking_classification.py:

Line 180:80: E501 line too long (82 > 79 characters)

• In the file mlxtend/classifier/tests/test_stacking_cv_classifier.py:

Line 464:80: E501 line too long (89 > 79 characters)

Comment last updated at 2020-04-04 04:33:47 UTC

[rasbt]

Sorry about that. Sure, i can restart it. However, I have seen this a couple of times recently. Let me try a little modification to see if it fixes it.

[nilichen]

Thanks! Do you mind taking a look at this PR first? I think it's already a lot of change changes. Gonna make another one for StackingRegressor and StackingCV if this one looks good to you.

[rasbt]

Thanks, and I will look at this soon! Sry, things are a bit crazy here due to the transition to online teaching etc. Will get back to this as soon as the more pressing things got sorted out

[nilichen]

Ah. No worries. Take your time!

…

On Fri, Mar 13, 2020 at 9:55 AM Sebastian Raschka ***@***.***> wrote: Thanks, and I will look at this soon! Sry, things are a bit crazy here due to the transition to online teaching etc. Will get back to this as soon as the more pressing things got sorted out — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#670 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ACFAWHZA7S4G7K3GSEFCYFDRHJQR3ANCNFSM4LGV2FPA> .

[rasbt]

Thanks again for the PR. I made some minor updates but it looks great overall.