tpm.r

library(dplyr)

counts = data.frame(Gene = c('A', 'B', 'C', 'D'),
                    Length = 1:4,
                    do1 = c(10, 20, 30, 40),
                    do2 = c(20, 40, 60, 80),
                    do3 = c(20, 20, 30, 40))

tpm = counts %>%
    mutate_each(funs(. / Length), starts_with('do')) %>%
    mutate_each(funs(1e6 * . / sum(.)), starts_with('do'))

tpm