Submitted by: Matt Dowle; Assigned to: Nobody; R-Forge link

1L="first"
.N="last"
sample(.N,size=1) = "random" (original proposal)
-1L = all but first
c(FALSE,TRUE) # even rows

http://r.789695.n4.nabble.com/What-s-your-opinion-on-the-feature-request-add-option-mult-random-tp4267483p4276880.html

but not expressions of column names in mult, leave that to .SD. For expressions of column names in mult, it would need to be passed through to dogroups.c and a more efficient .SD[i](evaluating i first in the special case of .SD[i]) seems a better way to do that, perhaps.