apply() and relatives

A discussion of apply, tapply, lapply, sapply, mapply, rapply, aggregate, by, split, rowSums, etc.

(and if time permits those distant relatives who should best be left locked in dusty attics: do.call and reshape)

No add on packages here, just straight R (though I may show some timing comparisons for the fun of it).

A BIG thanks to John for stepping in at short notice.