tools for splitting, applying and combining data

 plyr is a set of tools that solves a common set of problems: you need to break
 a big problem down into manageable pieces, operate on each pieces and then put
 all the pieces back together. For example, you might want to fit a model to
 each spatial location or time point in your study, summarise data by panels or
 collapse high-dimensional arrays to simpler summary statistics. The development
 of plyr has been generously supported by BD (Becton Dickinson).