*apply in all its variations …

Here is an excellent stackoverflow post on how *apply in all its variations can be used.
One of the followups points at plyr (from demi-R-god Hadley Wickham) which provides a consistent naming convention for all the *apply variations. I like plyr a lot, because like ggplot, it is easy to grasp and relatively intuitive to find an answer to even tricky problems.

Here is the translation from *apply to plyr …

Base function   Input   Output   plyr function 
---------------------------------------
aggregate        d       d       ddply + colwise 
apply            a       a/l     aaply / alply 
by               d       l       dlply 
lapply           l       l       llply  
mapply           a       a/l     maply / mlply 
replicate        r       a/l     raply / rlply 
sapply           l       a       laply