Apriori use sets

[WLaney]

Description

Changes apriori to return itemsets as sets instead of lists.

Related issues or pull requests

Disscused in issue 344

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

[coveralls]

Coverage increased (+0.01%) to 91.267% when pulling a7cdb41 on WLaney:apriori-use-sets into bcf3f44 on rasbt:master.

[rasbt]

Thanks for the PR!

I think for efficiency reasons, to avoid yet another for-loop, it would be better to do the transformation to sets some place earlier in the code. For example, replacing the line itemsets = pd.Series([set(i) for i in itemset_dict[k]] by

itemsets = pd.Series([set(i) for i in itemset_dict[k]]

and then the line for the use_colnames loop as well. I.e., res_df['itemsets'] = res_df['itemsets'].apply(lambda x: {mapping[i] for i in x}).

Would be great if you could also add a short unit test checking that the types of the itemsets is indeed "set" for use_colnames=True & False

Thanks!

[WLaney]

Thank you for the advice!

I tried to do the transformation earlier in the code on my first go, but I couldn't quite figure out where to do it without messing up the panda data structure. I was able to get it this time with your help though!

For the unit test I'm just looping through the returned itemsets and checking the type of each element. I've never had to make unit tests before, but I that test seems to checks what we want. If you think it would be better to do something else though just let me know.

[rasbt]

Could you change "defualt" to "default" ? :)

[rasbt]

I think this shouldn't be default behavior then, because the line above with "use_colnames=False" is indicated with default behavior

[rasbt]

That looks good, thanks! Could you maybe just do the little comment-fix that I mentioned above? Besides that, this looks good!

[WLaney]

Thanks! And yeah, no problem. Sorry about the comments, that was just carelessness on my part.

[rasbt]

That's great, thanks for the fix & PR