data(dietox)
summaryBy(Weight+Feed~Evit+Cu+Time, data=dietox, FUN=c(mean,var), na.rm=TRUE, use="pair")
orderBy(~Time+Evit, data=dietox)
splitBy(formula = ~Evit+Cu, data = dietox)
sampleBy(formula = ~Evit+Cu, frac=.1, data = dietox)
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