Hello everybody,
Data is
myd <- data.frame(id1=rep(c("a","b","c"),each=3),id2=rep(1:3,3),val=rnorm(9))
I want to get a cumulative sum over each of id1. trying aggregate does not work
myd$pcum <- aggregate(myd[,c("val")],list(orig=myd$id1),cumsum)
Please suggest a solution. In real the dataframe is huge so looping with for
and subsetting is not a great idea (still doable, though).
Thank you
Stephen B
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