Coursera: R Programming https://class.coursera.org/rprog-009
Programming assignment 1: https://class.coursera.org/rprog-009/assignment/view?assignment_id=3
Programming assignment 2: https://github.com/rdpeng/ProgrammingAssignment2
Programming assignment 3: https://class.coursera.org/rprog-009/assignment/view?assignment_id=7