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Weka now has support for the basic editing and execution of Groovyscripts. Groovy is a dynamic language, which allows you to quickly experiment with using Weka's core classes programatically. See also the Groovy scripting plugin for the Knowledge Flow.

Instance weights in the Explorer's Preprocess panel

Since instance weights can now be specified in standard ARFF and XML-based ARFF formats, the Preprocess panel of the Explorer has been upgraded to reflect information on weights and take weights into account for displayed statistics and histograms.