Another one I spent more time thinking on than I would like to admit! (The first into two -> in two, actually) :-)

In the end I differed to here: http://english.stackexchange.com/questions/75153/split-in-vs-split-into and http://english.stackexchange.com/questions/108335/split-in-half-vs-split-in-two-which-one-is-correct

In the first case we are dividing the data in half, so it's 'in', in the second case we don't know the piece sizes, so it's 'into'.