# NOT RUN {
DT = data.table(grp=rep(c("A", "B", "C", "A", "B"), c(2,2,3,1,2)), value=1:10)
rleid(DT$grp) # get run-length ids
rleidv(DT, "grp") # same as above
rleid(DT$grp, prefix="grp") # prefix with 'grp'
# get sum of value over run-length groups
DT[, sum(value), by=.(grp, rleid(grp))]
DT[, sum(value), by=.(grp, rleid(grp, prefix="grp"))]
# }
Run the code above in your browser using DataLab