R data.table binary value for last row in group by condition

Question

I have data like this:

library(data.table)
id <- c(\"1232\",\"1232\",\"1232\",\"4211\",\"4211\",\"4211\")
conversion <- c(0,0,0,1,1,1)
DT <- data.ta         


        

Answer 1

For each id, check if row number is the last row number in the group, and if 'conversion' is 1. Convert logical result to integer.

DT[ , lastconv := as.integer(.I == .I[.N] & conversion == 1), by = id]