search for: xcumsum

...ble) library(lattice) set.seed(123) mydt <- data.table(date = seq.Date(as.IDate("2024-01-01"), by = 1, length.out = 50), xgroup = "A", x = runif(50, 0, 1)) mydt <- rbindlist(list(mydt, data.table(date = mydt$date, xgroup = "B", x = runif(50, 0, 3)))) mydt[, `:=`(xcumsum = cumsum(x)), by = .(xgroup)] mydt[, lapply(.SD, sum), by = .(xgroup), .SDcols = c("x")] # xgroup x # <char> <num> #1: A 26.00455 #2: B 71.55405 #For xgroup = "B", line starts at the sum of all previous x values including xgroup = "A&quo...