library(data.table)
N <- 100
DT <- data.table(
id = 1:N,
v1 = sample(5, N, TRUE),
v2 = sample(1e6, N, TRUE)
)
sum_up(DT)
sum_up(DT, v2, d = TRUE)
sum_up(DT, starts_with("v"), by = v1)
sum_up(DT, by = v1)
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