I had something similar happen to me on a train. The guy didn't touch me, but sat across from me with his legs open and hands between his legs. Next thing I know his hands are moving much more than they should be. I felt disgusting. I reported and was told there is nothing that can be done about it because he wasnt doing anything illegal (bulls***!!!!!!!).
Having said that though, its a good idea to still report it. The more women that do the more the police may start to take some notice.
Chocolate is an ideal cure