require(data.table)
DT = data.table(a=1:1e8, b=1:2)
DT[,.N,by=a,verbose=TRUE]
# Detected that j uses these columns: <none>
# Finding groups (bysameorder=FALSE) ... done in 0.757secs. bysameorder=TRUE and o__ is length 0
# Optimization is on but left j unchanged (single plain symbol): '.N'
# Starting dogroups ...
# memcpy contiguous groups took 12.143s for 100000000 groups
# eval(j) took 13.800s for 100000000 calls
# done dogroups in 55.253 secs
# a N
# 1e+00: 1 1
# 2e+00: 2 1
# 3e+00: 3 1
# 4e+00: 4 1
# 5e+00: 5 1
# ---
# 1e+08: 99999996 1
# 1e+08: 99999997 1
# 1e+08: 99999998 1
# 1e+08: 99999999 1
# 1e+08: 100000000 1
