In core Weka

• Numerically stable implementation of variance calculation in core Weka classes - thanks to Benjamin Weber
• Unified expression parsing framework (with compiled expressions) is now employed by filters and tools that use mathematical/logical expressions - thanks to Benjamin Weber
• Developers can now specify GUI and command-line options for their Weka schemes via a new unified annotation-based mechanism
• ClassConditionalProbabilities filter - replaces the value of a nominal attribute in a given instance with its probability given each of the possible class values
• GUI package manager's available list now shows both packages that are not currently installed, and those installed packages for which there is a more recent version available that is compatible with the base version of Weka being used
• ReplaceWithMissingValue filter - allows values to be randomly (with a user-specified probability) replaced with missing values. Useful for experimenting with methods for imputing missing values
• WrapperSubsetEval can now use plugin evaluation metrics

In packages

• alternatingModelTrees package - alternating trees for regression
• timeSeriesFilters package, contributed by Benjamin Weber
• distributedWekaSpark package - wrapper for distributed Weka on Spark
• wekaPython package - execution of CPython scripts and wrapper classifier/clusterer for Scikit Learn schemes
• MLRClassifier in RPlugin now provides access to almost all classification and regression learners in MLR 2.4