dekay.org

"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. It's already possible to do this with split and the apply functions, but plyr just makes it all a bit easier with: * consistent names, arguments and outputs * input from and output to data.frames, matrices and lists * progress bars to keep track of long running operations * built-in error recovery The aim of this release is to provide a consistent and useful set of tools for solving the split-apply-combine problem. It is not particularly fast or memory efficient, but there is much potential for optimisation, particularly by rewriting important bits in Ⅽ."