R, caret, and Parameter Tuning C5.0

Boosted C5.0 classifiers are known to perform well when stacked up against other classifiers (see, for example, this paper). 

The caret library for the R programming language is an exceptional environment for automatic parameter tuning and training of classifiers. However, caret does not allow for out-of-box tuning of C5.0 tree complexity. This post shows how you can customize caret to do just that.