Cumulative total by group

Question

For the following dataset:

d = data.frame(date = as.Date(as.Date(\'2015-01-01\'):as.Date(\'2015-04-10\'), origin = \"1970-01-01\"),
               group = re         


        

Answer 1

Is this it?

sp <- split(d, d$group)
res <- lapply(seq_along(sp), function(i) cumsum(sp[[i]]$value))
res <- lapply(seq_along(res), function(i){
        sp[[i]]$c.sum <- res[[i]]
        sp[[i]]
    }) 
res <- do.call(rbind, res)
res