plot_gbm plots the fitted values against the real values
gbm_plot(x)
A ggplot2 plot
This is a development function that aims to improve the default plots used in gbm.step by elith et al. Their plots are good, but I want them to be better. In the future, this might even be implemented in ggvis. NB: This currently only works for gbm.step functions. In the future more features will be added so that it works for many decision trees.