[R] Identify first row of each ID within a data frame, create a variable first =1 for the first row and first=0 of all other rows

[Boris Steipe]

olddata$first <- as.numeric(! duplicated(olddata$ID))


:-)




> On Nov 30, 2024, at 22:27, Sorkin, John <jsorkin using som.umaryland.edu> wrote:
> 
> 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))
> olddata <- data.frame(ID=ID,date=date)
> class(olddata)