Free Carpentry R Resources
Data Carpentry and Software Carpentry are sister organizations devoting to helping people automate their research. Data Carpentry focuses more on working with data (dataframes, data manipulation, visualization) while Software Carpentry emphasizes programming best practices (writing functions, vectorization, etc.).
Both organization run two-day workshops you can attend in person, but they also make their lesson material freely available online. See here for an intro to R from Data Carpentry and here and here for an intro to R from Software Carpentry.