r - Cumsum with plyr ddply is not keeping running total -


i'm trying use cumsum, plyr's ddply have running total. however, don't understand why not work.

n = c(2, 3, 5)  s = c("aa", "bb", "cc")   dd = data.frame(n, s) #   n  s # 1 2 aa # 2 3 bb # 3 5 cc  test <-ddply(dd, "n", transform, ttl = cumsum(n)) #   n  s ttl # 1 2 aa   2 # 2 3 bb   3 # 3 5 cc   5

what expect ttl should is:

#  2 #  5 # 10

it'd great if explain i'm doing wrong here , how can obtain desired result. thanks.

as mentioned in comments, ddply works completly fine.

however think want ttl cumulative sum of n. use (also simpler) code:

dd$ttl <- cumsum(dd$n)

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