Make stacking estimators capable of replacing base estimator in searchcv

[qiagu]

Description

• Introduce multiple processing to StackingCVClassifier
• Apply _BaseXComposition to StackingCVClassifier
• Apply _BaseXComposition to StackingClassifier
• Apply _BaseXComposition to StackingRegressor

Related issues or pull requests

#517
Make Stacking classes capable of replacing regressors/classifiers in GridSearchCV

Fixes #517

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 nosetests ./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., nosetests ./mlxtend/classifier/tests/test_stacking_cv_classifier.py -sv)
• Checked for style issues by running flake8 ./mlxtend

[pep8speaks]

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

There are currently no PEP 8 issues detected in this Pull Request. Cheers! 🍻

Comment last updated at 2019-04-28 05:07:16 UTC

[coveralls]

Coverage decreased (-0.03%) to 91.547% when pulling 315034b on qiagu:stackingcv into a3a539e on rasbt:master.

[qiagu]

Sorry, the safe_indexing is gone in this PR, but we'll gain somehow multiple processing feature.

[qiagu]

@rasbt I didn't figure out how to update the docs under the api_modules. Could you please have a look? Otherwise, I would like to stop here.

[rasbt]

Looks amazing! Thanks a lot! It's a bit unfortunate that the safe-indexing has to go, but yeah, multiprocessing is probably the more useful one here.

Regarding the API modules, all you need to do is to

1. cd into the mlxtend/docs subfolder and then run python make_api.py
2. Run the last cell in the respective notebook which reads in the api doc file

I am happy to do that if it doesn't work.

[qiagu]

It worked. Thank you. @rasbt
I can attest that the make_api is a great design.

[rasbt]

Awesome, thanks! Looks got to merge to me, unless you have anything else in mind that should be added.

I can attest that the make_api is a great design.

thanks :). Haha, I remember that it took me quite some time to get that one working properly :)

[qiagu]

The make_api script is super cool!
I don't have anything in my mind for now. I appreciate you merging this. My tool will have new wheel.

[rasbt]

Alright, will merge then. Again, thanks a lot for this very nice PR!