Fast alternative to split in R

Question

I\'m partitioning a data frame with split() in order to use parLapply() to call a function on each partition in parallel. The data frame has 1.3 m

Answer 1

Split(x,f) is slow if x is a factor AND f contains a lot of different elements

So, this code if fast:

system.time(split(seq_len(1300000), sample(250000, 1300000, TRUE)))

But, this is very slow:

system.time(split(factor(seq_len(1300000)), sample(250000, 1300000, TRUE)))

And this is fast again because there are only 25 groups

system.time(split(factor(seq_len(1300000)), sample(25, 1300000, TRUE)))