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[R-Forge #2722] optimize j=c(lapply(.SD,sum),.N) #370
Submitted by: Sam Steingold; Assigned to: Arun ; R-Forge link
As reported here.
options(datatable.warnings = TRUE) dt <- data.table(a = c(rep(3, 5), rep(4, 5)), b=1:10, c=11:20, d=21:30, key="a") dt <- dt[, c(lapply(.SD,sum),.N), by=a]
results in an optimisation warnings, so I cannot discard the original table right away and have to resort to an intermediate one:
dt.out <- dt[, lapply(.SD, sum), by = a] dt.out[, count := dt[, .N, by=a]$N]