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.
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