Re: [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

[Christopher W. Ryan via R-help]

Personally, I'd do this in the tidyverse with dplyr and its row_number()
function.

olddata %>% group_by(ID) %>% mutate(first = as.integer(row_number() == 1))

--Chris Ryan

Sorkin, John 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)

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