In addition to many good solutions already provided, this solution uses
data.table package.
library(data.table)
mydf <- data.frame(id = c(rep(1,10),rep(2,6),rep(3,2)), date =
c(rep(1,2),rep(2,2),rep(3,2),rep(4,2),rep(5,2), rep(5,3),rep(6,3),rep(10,2)))
setDT(mydf)
mydf[, `:=`(firstdate = with(.SD, min(date))), by = .(id)]
setDF(mydf)
On Nov 27, 2024, at 11:30 AM, Sorkin, John <jsor...@som.umaryland.edu> wrote:
c(rep(1,2),rep(2,2),rep(3,2),rep(4,2),rep(5,2),
rep(5,3),rep(6,3),rep(10,2))
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