R 3.3 - Access or Create Columns in Data Frames, or Simplify a Data Frame using aggregate()
Channel: Google for Developers
Date: 2013-07-01

The with() function makes it easy to access many variables (columns) in a data frame for one-off calculations, the within() function can be used to create new columns that are merged with the original data frame, and aggregate() is useful for aggregating variables in a data frame across groupings based on one or more variables.