Re: [R] Data framing question

Hi, You may also try: library(data.table) dt1 <- data.table(dat1, key = "identif") dt2 <- copy(dt1) dt3 <- copy(dt1) dt1[,c("roa1", "eta1") := list(c(NA, roa[-.N]),c(NA, diff(eta))), by=identif] #or dt2[, `:=`(c("roa1", "eta1"), list(c(NA, roa[-.N]), c(NA, diff(eta, by = identif] # or dt3[,

Re: [R] Data framing question

Hi, May be this helps: dat1 <- read.table(text="identif roa eta 1 7 5 2 8 9 2 9 8 2 10 7 3 11 6 3 1 4 3 2 2 4 3 3 4 6 5",sep="",header=TRUE) dat2 <-within(dat1, {     eta1 <- ave(eta, identif, FUN = function(x) c(NA, diff(x)))     roa1 <- ave(roa, identif, FUN = function(x) c(NA, x[-length(x)]))