I'm very new to text mining. I am trying to build a classifier which assigns zero, one or more topics to each document of the Reuters 21578 dataset. However, I'm not sure how to make it work using standard R packages. I've looked at a lot of simple online examples using packages such as RTextTools and RWeka, etc. which creates classifier to assign one topic to each document and I'm stuck as I can't directly follow the examples to achieve what I desire. Thanks in advance!  
Text classification: how to assign 1 or more classes to each document?
machine learning;r;text mining