I have used Random forest and ANN based prediction models for my study. But, I am unable to find any code for R/RStudio (though i have tried some, but they are not giving any results) related to variable importance or relative variable importance. Further in my studies, I am planning to use SVM and KNN too, so if there is any code which will be globally effective to all the models or codes which are suitable for individual model (RF, ANN, SVM, K-NN) will be greatly appreciated.