Best R tutorial/book for Machine Learning

I am in a ML and Data mining class right now and we are encouraged to use R for our assignments and projects. I've been using Weka with my supervisor.

I have a decent coding background but I wasn't able to understand the syntax of R so I need to find a good tutorial or book to help me learn, probably from the near begining.

In our first assignment we were supposed to use RWeka and DMwR libraries but even after seeing the solution I still don't understand the code and syntax.

For our project we are to be pre-processing lots of text (which I could easily do in python) and then do ML on it to improve the classification rate. Since it is imbalanced data (10-90) I know I need to deal with stuff such as the area under the curve (which I can't do in Weka).

So please recomend me a good tutorial or book I can get to help me learn the syntax for R that touches upon ML related tasks.

Thanks