# NOT RUN {
# load the dataset
data(leukemia72_2)
# X95735_at
with(leukemia72_2, by(X95735_at,Class,mean))
# M27891_at
with(leukemia72_2,tapply(M27891_at, Class, FUN = mean))
with(leukemia72_2, table(M27891_at=ifelse(M27891_at<=mean(M27891_at), "1", "2"), Class))
# }
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