New Features New function implementing the resampled paired t-test procedure (paired_ttest_resampled) to compare the performance of two models (also called k-hold-out paired t-test). (#323) New function implementing the k-fold paired t-test procedure (paired_ttest_kfold_cv) to compare the performance of two models (also called k-hold-out paired t-test). (#324) New function implementing the 5x2cv paired t-test procedure (paired_ttest_5x2cv) proposed by Dieterrich (1998) to compare the performance of two models. (#325) A refit parameter was added to stacking classes (similar to the refit parameter in the EnsembleVoteClassifier), to support classifiers and regressors that follow the scikit-learn API but are not compatible with scikit-learn's clone function. (#325) The ColumnSelector now has a drop_axis argument to use it in pipelines with CountVectorizers. (#333) Changes Raises an informative error message if predict or predict_meta_features is called prior to calling the fit method in StackingRegressor and StackingCVRegressor. (#315) The plot_decision_regions function now automatically determines the optimal setting based on the feature dimensions and supports anti-aliasing. The old res parameter has been deprecated. (#309 by Guillaume Poirier-Morency) Apriori code is faster due to optimization in onehot transformation and the amount of candidates generated by the apriori algorithm. (#327 by Jakub Smid) The OnehotTransactions class (which is typically often used in combination with the apriori function for association rule mining) is now more memory efficient as it uses boolean arrays instead of integer arrays. In addition, the OnehotTransactions class can be now be provided with sparse argument to generate sparse representations of the onehot matrix to further improve memory efficiency. (#328 by Jakub Smid) The OneHotTransactions has been deprecated and replaced by the TransactionEncoder. (#332 The plot_decision_regions function now has three new parameters, scatter_kwargs, contourf_kwargs, and scatter_highlight_kwargs, that can be used to modify the plotting style. (#342 by James Bourbeau) Bug Fixes Fixed issue when class labels were provided to the EnsembleVoteClassifier when refit was set to false. (#322) Allow arrays with 16-bit and 32-bit precision in plot_decision_regions function. (#337) Fixed bug that raised an indexing error if the number of items was <= 1 when computing association rules using the conviction metric. (#340)