[R-Forge #2722] optimize j=c(lapply(.SD,sum),.N)

[arunsrinivasan]

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]