Apply-style commands in R

Here's a quick table of what I think are the most useful apply-style commands in R: Function Input Output Best for apply Rectangular Rectangular or vector Applying function to rows or columns lapply Anything List Non-trivial operations on almost any data type sapply Anything Simplified (if possible) or list Same as lapply, but with simplified output plyr::ddply data.frame data.frame Applying function to groupings defined by variables For alternatives to plyr, see this post on StackOverflow.